My knees were just too far forward, they weren't tucked in the frame they were hitting where it curves out. The change I made pushed me back about 2 inches, which is more than enough. I just test road it with the additional foam and it's good to go, I just need 1 thin layer of some dense closed cell foam and off to the upholstery shop for some new vinyl.
Curious how tall you are/inseam length. People warned me I wouldn't fit on the bike at 6'1 (32 in inseam) but i have loads of room before i get near to the flare of the frame.
Where did you/will you source your foam? I have an RD350 project i'd like to try to make a slopeback (all foam) seat for on the stock pan.
Base foam is carpet padding, free scraps from a local store, spray adhesive to attach (3m 90) and then shaped with 80 grit and pneumatic die grinder... should have used 100 grit but only had 80 and lower. Top layer is coming from https://www.sunmatecushions.com/ and I am 34"-35" inseam