I've just started restoring one of Ron R. Boi's frames. It's not in great shape, as it has been sitting somewhere on his farm for about 10 years. Ron sandblasted rust from the top tube where someone had removed the braze on cable tunnels. There is some minor rust on other areas, which I've mostly removed. The seat lug had been chipped and had a bunch of rust, so I filed that out and thinned it a little.
The bottom bracket shell is massive. It looks like it could be a plumbing fixture! It's contributing probably 40% of the frame's weight.
At least some of the lugs are Bocama of France (BCM) Professionals (short point). BCM happen to be my initials...
Super Vitus 971 tubeset
I wasn't sure what XC35 was, besides being a carbon steel of some kind, obviously.
From the french AFNOR standards, I'd call it a medium carbon manganese steel.
Good mix of stiffness and durability.
C Si Mn Smax Pmax
TU XC 35 0,30-0,40 0,10-0,45 0,40-0,90 0,04 0,04