Oops. I misread this as 56. Maybe because I am working on my 56 tail lights. I don't know if the gaskets are similar on the 55 so the items mentioned may not apply.

I just replaced the round foam gasket on the housing with McMaster:
1298N2 Multipurpose Neoprene Foam Cord, 3/16" Diameter, 15 Feet Long.
I used 3M super weatherstrip adhesive to attach it.

I haven't redone the lens gaskets, but for the front parking light lens gaskets I got from McMaster:
86025K42 Ultra-Conformable Light Duty Vinyl Foam Sheet Sheet, Ultra-Smooth Texture, 1/8" Thickness, 54" WD, 1 ft. Length
I'm still in the process of making the gaskets.

Continental still lists belts on their web site:
http://www.showmetheparts.com/partfinderelitemobile/
The fan belt is the 15574. I have it installed on my '56.

I purchased a reproduction gas tank from Auto City Classics, https://autocityclassic.com/, last April. At the time they said they had a lot of them in stock. It did have the problem that the filler pipe opening wasn't in the correct position behind the filler door. It only required a little additional bend be added to the first two bends as measured from the tank. I have had no problems with the tank.

The Subaru brake light switch is mechanically operated by the brake pedal and not connected to the hydraulic system.

Why not try some new technology to solve the problem.
Take off one of the good ones and have it 3d scanned. There are a number of 3d scanning services in the Sydney area.
Not familiar with 3d scanning, here is a segment from Jay Leno's Garage:
https://www.youtube.com/watch?v=n60NibYbPqQ

Then you can have the resulting model sent to a 3d printing service and make as many as you would like. One of the nice things about having a 3d model is that you can send to anyone that needs it.
Here is another clip from Jay on Direct Laser Metal 3d printing:
https://www.youtube.com/watch?v=bwFspzVGUF4

Objective 3D in Melbourne offers printing services
www.objective3d.com.au

While I don't have anything with him at the present time, he did rebuilt the Autolite distributor for my '56 Clipper. It looks good and works well. He had it for 10 months from Sept 2016 until July 2017, It was waiting in line for the majority of that time. I do not have the actual time split between being in line and being rebuilt.

The real benefit of the J-5992 is for removing the damper as it reaches around to the back half so as not to stress the rubber.

When I got mine, it was missing the center adapter J-5992-2. For removal I just backed out the retaining screw and let the screw assembly J-5992-3 push against it.

For installation, the spacer just makes the nut used to press on the damper accessible. The spacer J-5992-4 dimensions are 2 3/4" long, 1 3/4" OD, and 7/8" ID.

PPG Paints has a Color Library which has the old formulas which they can look up using the original paint codes and convert to their current pigments and chemistry. Their number is (800) 647-6050. They will only give the new formula to one of their authorized dealers to mix the paint, but you can call them to make sure they have the information on your color.

I had them match Adriatic Blue for my steering column shift collar and Danube Blue for my wheels. While they are not a perfect match to the old paint, in my case the newly painted parts are in locations where it is hard to compare them.

Unfortunately I was doing the have it rebuilt when you take it off method so it has been a couple of years. I think they used the original impeller. There isn't a list of parts replaced on the invoice, only a note (plastic impeller).

Where did you get the stainless impeller? Is someone making replacement impellers? What about the cast impeller? I understand that you can use one from a Hudson pump.

Thanks.