Hi, Got the exact same RC100 here. To answer the front mech question it did not have a f/mech mount welded on. What you had was an old style Shimano endless band front mech which is bent square instead of round. Then there is a metal shim, flat one side where it butts against the frame and round the other side to fit against the mech. I've got all the bits here, not for sale im affraid, but mail me at email@example.com
if you want pics. Should be easy to get something made up.
Good luck with the rebuild. I also have a .jpg here of the original stickers if you want it, cannot remember where I got this from, maybe this thread ?, dont want to steel the credit from someone else.