The biggest problem with the brake system is that the DOT 3 brake fluid is alcohol based and the cap of the master cylinder vents to the air. Over time, atmospheric pressure and temperature changes cause air to enter and leave the brake system through this vent hole. The vent is necessary because of changes in the volume of the master cylinder when you apply and release the brakes, but the air entering and leaving the master cylinder brings moisture in with it, which readily unites with the alcohol in the brake fluid. When enough has entered, it begins rusting the brake system from the inside out.
I wasn't successful at finding a modern style master cylinder which is sealed and not vented that would also fit my Truckster, so I decided to just replace it with a new original and then replace the DOT 3 brake fluid every couple of years with new brake fluid. They now make brake fluid that is silicone based and doesn't have this affinity for moisture, but it is not compatible with the old DOT 3 fluid or the rubber parts of the existing brake system. Well, it was an education, but a dead end, so I just decided to replace the DOT3 fluid every 2-3 years.
Make certain that you put an inline fuel filter between your gas tank and electric fuel pump. Even small amounts of rust and debris will kill an electric fuel pump. Do it even after re-lining your tank.
I think your fuel pump will be OK with the fuel pressure. The deciding point will be how well the needle valve attached to the float in the carburetor can hold back the pressure. A new carburetor float and needle valve are going to be a "must have". If gas ever starts coming out of the float bowl vent, either the needle valve isn't closing completely, or the fuel pump pressure is too high.
Is your gas tank rectangular and attached to the side of the frame on the left? If so, it is the same as mine, and the relining kit for a 5 gallon tank is adequate. Once open, you can't save any of the epoxy-like relining material. It begins hardening as soon as air gets to it. There will be some left, but it isn't worth keeping. Use it all and trash what you drain back out after sloshing it all around to be certain of covering all inside surfaces.
For some interesting reading covering a lot more, do a search on my posts and read about my suggestions to help others. It will save me a whole lot of typing.
Don't hesitate to ask more questions here, if you should need to know more. The service manual is available on the
www.sillylittlecars.com website too. (I'm a member there). The "supplement" manual contains the electrical schematics and also the OMC motor information. The main manual is the exploded views and parts lists for the body and frame, of which most of the parts are no longer available.
Please post a few photos. I would love to see what you have. I'm in South Central NC just above Charlotte, NC. Are you near me?
Charley