None of the hardware stores near me carry brass in a size that would work.
I ended up getting an OEM new petcock from David Silver Spares and this new valve is doing the same exact thing as the old one.
Additionally, I confirmed that this whole fuel issue is partially related to the petcock. The lack of fuel being transferred to one bank of the carbs is obviously a major issue, but the carbs that DO get fuel and dumping it is another part.
I got reproduction floats from 4into1.com and though they are pricey for repro I will say it doesn't seem like there's too many variables for it to make or break the project and the new hardware operates like a dream in comparison. It was definitely worth it. Ever since I replaced those, no fuel dumping, no leaks, no draining into the overflow tubes!
While I waited for the new petcock to come in the mail, I decided just to use a plastic jug gas tank meant for use with carb synchronization, and see how the new floats performed. I connected it to both banks just using a plastic T fitting and sure enough I was finally able to get the bike stable and idling confidently.
Got my first test ride in and noticed a few issues. 1, forgot to tighten down and adjust the clutch cable, so I was only able to get it to hold gear shifts downhill. I only tested 1 and 2. 2, I made new fender brackets to mount my fender closer to the tire and it intermittently rubs the tire. I have been watching and checking and it doesn't seem to be the brackets or the fenders moving, so now I am worried the wheel is perhaps bent or if its not mounted evenly? But it looks even and the axle looks fine in the fork body mounts. Perhaps the fork bodies are rotated a bit and not facing perfectly left and right?? I had these wheels balanced at a reputable shop so I'd like to think if there was any chance of a bent rim they would have noticed and said something.
But most importantly of all, another leak has appeared... Right side crank seal.
Looks like the seal itself ovaled out. You can't really see it in the picture, but I could see the inner diameter of the seal at the bottom of the crank snout.
You can see the buildup here as well as it also trailing straight down the casing.
I posted about it on some FB pages and asked a few forum members for advice and right now, we are going to try reinstalling the seal without splitting the cases. Enough people told me they had to do this job plenty of times on their 500/550, so I'm willing to try it first. We have high quality seal installation tools at work and they are letting me borrow them for the job so I'm hopeful.
I ordered 2 new OE seals from David Silver Spares so that if one method doesn't work, we have an extra one waiting. I also ordered a left one just in case, haven't inspected that side yet though. We removed the failed seal using the wood screw trick.
Here's what it looked like before we cleaned it. I used Q tips and gas and brake cleaner on the Q tips and cleaned them to the point that no more dirt is appearing on the cotton. Will reclean when seal is here.
The seal kit I used to assemble the bike was the kit from 4into1.com in case anyone is wondering. I ordered it out of convenience/ being noob friendly, however if there's anyone building their CB and reading this I would recommend just taking the part numbers out of the description of the kit and ordering OE. I don't know what caused this failure but I think failure would have been less likely had this seal had a lip like OE does.