Two assumptions regarding the following: your timing is always too retarded, and you have the type of dizzy where the vac advance twists the whole thing. If you have a Delco that doesn't twist with the vac advance then you can rotate the dizzy any where you like by loosening the horizontal clamp screw on the retainer plate. Otherwise:

Turn the engine to the correct timing mark, # 1 ready to fire. Pull the dizzy out an inch or so. Take out the two long bolts that retain the oil pump (1/2 inch heads) . Pull the oil pump absolutely straight out and note carefully by eye or with a marker where the gear is. Move it very carefully one tooth to the right. Push the pump absolutely straight back in and bolt it down. Now push your dizzy back in and it should settle slightly ccw from where it was. Set your timing per my video--you should be in the center of the adjustment range.

Retarded timing on these flatheads absolutely kills their performance and make them run scorching hot.

That sensation--freewheeling, should only be noticeable below the overdrive engagement speed of twenty-something mph. If that is what you are getting above that speed, then the overdrive is not working.

From whence the firewall pad? I need one too.

Preload of the worm bearings is controlled by shims at that lower plate. I know on the later cars the shim pack doubles as the gasket for the plate; the gasket is made of multiple thin plies that one may remove as necessary. 39 I don't know, but the shim may just be a ring of paper or steel that is placed in the end of the housing bore before the cover is installed. They need to have a right fair preload on them that is noticeable when turning the shaft by hand.

Another source of play in high mileage cars is the sector gear moving in the sector as those thrust bearings have worn. That will take some creative disassembly and shimming if that is the case.

Maybe lay a ruler next to them to gage the size. They look like the hold down bolts for the front motor mount on a forties Chrysler product.

For those who might think the interior is not correct, the parts book tells me that tan leatherette or tan leather was available as an option on the Eights. Very cool. I like it. But can't buy it.

Ghandi was wrong. Violence is the answer. But before that, mark your yoke, the nut, and the shaft with a punch or whatever so you can put it back exactly the same as it was to preserve the preload on the bearings.

yes, you will need to use the large pilot bearing from the 49-56 engines.

Regarding your heat riser: the remnant of your counterweight indicates that it is in the up, or closed position. That puts a lot of heat on the carb. Take two small hammers and tap the shaft forward/back, forward back till it is free enough to turn. Turn it down and then unhook the spring in the front. In the summer you can easily live without it.

To use the later engine you have only to transfer over the mounting details from your old engine: water pump, front plate, motor mount arch etc. Gives you a much larger pool of engines to fish in.