Believe you hit upon the reason BTV can get away with 1:1. It does not have a piston in the conventional sense. Actual dimensions are on the forum somewhere, but the "cylinder" is a chamber filled with fluid around an inch in diameter. One end has the "piston" which is a rod around 3/4" diameter but does not touch the cylinder walls. As soon as the pedal is moved, the compensator valve closes trapping the fluid. The only place fluid can go is to the wheels when the rod is pressed further in to displace it. How far pedal moves depends on wheel cylinder/shoe adjustment, but since it is a narrow rod with a long travel, that provides the advantage and volume.

Conventional masters have all the fluid pushed ahead of the piston and since there is a greater surface diameter, more volume with a shorter stroke is obtained at the expense of mechanical advantage due to that same large surface area having to push all the fluid instead of just displace or squeeze it out. Hence the need for a higher mechanical advantage at the pedal to achieve the output pressure.

The 7" booster is larger than the BTV and will provide more assist, all other factors equal. Those with math skills can work out the actual boost but the disadvantage again comes due to the short travel and large piston vs small piston and long travel in the BTV.

There are other products similar to the inline boost you mention but again, they just provide a slight addition to what is there to start with.

Looks like it might work. The original has the feed wire on one stud and the other stud is attached to a buss bar on the light switch which provides the mounting. The extra mounting screw tabs on that would not be used and if they don't interfere, all is well. If they do, then not a big job to mount the breaker close by and just run a short decent ga wire to the buss bar.

If you haven't already, suggest downloading the service training manual on the econodrivehttps://www.packardinfo.com/xoops/html/downloads/EconoDriveTrainingBook.pdf There is a schematic and halfway decent description of the R-9 electrical operation.

Obviously, replacing or repairing the original relay assy would be preferred but if that's not practical, it MIGHT be able to be replaced with a pair of modern relays and keep the wiring intact. Actuating relay 1 could be substituted with another capable of carrying the current such as the Bosch and solenoid could be made to work similar to R11 --but 2 caveats.

In the current system, the pull in and hold in coil are both fed from terminal 4 when governor and other switch logic allows relay 1 or actuating relay to engage. The wire to hold in coil at relay is actually terminal 3 but that is fed internally from 4 by being in series with the second relay coil and means that relay also pulls in. It's function is in completing part of the ground out circuit and was eliminated in the R-11. The first kicker comes in determining whether the R-9 solenoid hold in coil could handle being hooked up directly to voltage without that second relay coil in series or if it would overheat. It should be possible to add a resistor if one of sufficient wattage and resistance to the original second relay coil can be easily found if it looks like that may be a problem.

The contact logic of the original assy could be bypassed and almost duplicated with a second Bosch relay. It's coil would be parallel to relay 1 so both actuate at the same time. (Two Bosch singles are much cheaper and easier to find than a DPDT relay with proper specs.) That second relay only uses the normally closed contact to control the ign ground out circuit in conjunction with mechanical contact in solenoid. That is the other kicker because it would have to be determined that mechanical contact stays open when solenoid is not energized since the open series contact in the original second relay is now gone. The R-ll runs the ground out circuit thru the kickdown switch instead of second relay to ensure it stays open when not in use. To do that on yours would require an R-11 switch and wiring changes.

The solenoid will determine if you can do something without using the original relay so the main question is electrical and if something you wish to pursue, could be investigated. I don't think the R-9 solenoid can be replaced with the later one but perhaps someone with both units can compare mounting and plunger length to answer that.

While 3 per side would have been standard on the convertible 250, there are pictures in various books & magazines showing 4 on various models. 4 from the factory would normally be only on the 400 according to the parts book. They were available from the dealer for something like $2.50 each so a cheap dressup. Also possible they were requested to be removed vs a shoddy repair.

If you want to add them back, should be able to find them from parts cars as they were used on lots of models. Next time you view the car, open the trunk and see if there are signs of a proper removal with neatly welded in holes or something else. It's even possible a back end from another car never having any was installed if it had been hit. As O_D said, they came and went and more important would be the condition and correctness of the rest of car.

My original article is herehttps://www.packardinfo.com/xoops/html/downloads/FuelFilterMod.pdf but someone came up with a way to do it and didn't use the emt conduit ring. Can't remember who or what he did though.

I didn't make another but did think of an easier way to make a ring. Use a length of .016 or .025 x 1/4" wide brass strip available at the hobby shop and solder in a circle.

The original filter I made is still in use and working fine after 3 yrs.

The larger diameter won't fit at the top. It is just wide enough that it won't clear the available spaces and drop down in the recesses to seal against the gasket.

If I can still find it, will take a comparison picture. Vaguely recall possibly throwing it away so maybe not. That's why I came up with first version of the paper replacement because I couldn't find another at the time and wasn't smart enough to think of a tractor place--even though I'm in the middle of farm country.

If it's the one labeled 30-87 fuel filter carter ceramic for 7.00 plus 6.40 shipping, believe it's the tall one and don't think it will fit the glass. Believe there is also about a 1/4 inch larger diameter element but approx correct height which won't fit either. Have seen that available (the shop that rebuilt my carbs sent one) in some places so watch out for it as well.

Glad it worked. Just curious if you know-- did they have it ready on the shelf or make kits up special for your friend?

Looks a lot like the Packard plant, doesn't it.

Seems strange with all the stories one would read over the decades of Soviet people having nothing or just barely making do and having to adapt one thing to do another that they let it rot & didn't find another use for the place. Any idea when this one closed.

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Glad the wood was saved when it was but you know it's getting old hat when fire news is only an aside comment in another post. The pictures on the Detroit websites show a pretty good blaze going but guess it's mostly out again now.