Tripeds are rad AF, glad to see another one getting some love!
Bummer about the gas tank. I would recommend an aluminum tank from Sandstorm. They have a huge selection, choice of finish, and can include many of the necessary accessories (petcock, cap, cap with gauge, reserve tank partition, clamps, etc.). You have a first gen, second revision body/frame style so the tank won't be quite the same as the one that I used as it will need to fit within that frame clearance. Link if you want to go that route.
The hydro front end made a huge difference, and you have taken it to another level with disk brakes; nice work!
I am having issues with the drive chain on mine, and need to add a secondary tension point with a roller guide or something to keep the chain from throwing itself off. Such a long run on these things. I have also found that a 415 HD chain doesn't match the rear sprocket so I need to source a chain that matches the pitch as the stock chain is in need of replacement, but it looks like you have alleviated that issue.
I look forward to seeing the progress. Keep up the solid work!