I remember seeing these frames in the early 1990s at races on the Isle of Man. They were made for the 3YL & early 4DP TZs I believe and made to be much stiffer for the bumps and jumps in pure road racing. ie IOM TT / MGP / NW200, as oppose to the silky smooth GP tracks the standard frame worked best on. Interesting to see one for the RS.

Good luck with the build.

Cheers

Dan