Hi! I just came across this nice road bike frame and I could not figure who made it. Maybe you can help me out?

It is a quite lightweight frame with some very nice details. Apparently it has been repainted by a paint shop or factory "approved" by Columbus (see "riverniciato" stickers). It has chromed forks and Gipiemme dropouts and some engravings as well but I can not figure what letter/logo is that (K? R? F?). The RGF bottom bracket shell made me think it was a french frame. It also has some "SHIMANO" decals but I don't think that is relevant.

Some photos:


Any ideas?

Thanks!