I wanted to provide an update for this thread. My friend completed the fabrication of the replacement steel tube. I found a replacement spring online made from 302 stainless steel. I matched the diameter and wire size. I figured the length was within a 1/4 inch. I had no idea about the spring rate or max load. In the end, I wasn’t too worried about the spring specs, given the tension can be adjusted.
We tried some test solders, using paste flux and stay-brite silver solder (probably 8% silver), on some scrap parts and failed initially. I did some research and paste flux is not the way to go for soldering steel. I purchased the Harris solder kit with the Stay-Clean liquid flux and Stay-Brite silver solder. I did a couple more test solders on scrap parts using the kit flux and solder, and everything worked ok. I soldered the steel tube to the valve nut and thankfully it went great. I cleaned the flux off and installed the pressure relief valve back into the engine. The initial oil pressures were promising even after the engine warmed up – around 20 psi at idle and 40 psi at higher rpms. I adjusted the bolt on the pressure relief valve to increase spring tension and ended up with high 30s psi at idle and low to mid 40s psi at higher rpms. Given I have no idea how accurate my oil gauge is, I took those specs as a victory! I knew I needed to seal the adjustment bolt to prevent oil leaks. I tried counter sinking the locking but and using rubber washers with no luck. The washers kept getting squeezed out when the locking nut was tightened. I ended up using a sealing washer and it seems to be leak free. I changed the oil and filter to get rid of any crap that might have been freed up. Post oil change, the pressures are still looking great.
I think I am missing the washer that sits under the pressure relief valve head. Hopefully, that should be simple to address. It is unclear if the lack of a washer is causing an oil leak or not.
I took the car out for a short drive in my neighborhood tonight. It was the first time the car had moved in over 8 years. I’m stoked. 😀
Thanks for all the advice.