For a mutt-campagnolo grouppo I think the frame should be italian. I think that very few non-italian company made bikes with mid-level italian components.
Some italian manufacturers making bikes with gransport or valentino stuff in the 1970's were atala and frejus. you don't want to hunt up an atala - unless you are interested in a bargain on a rust-bucket frame. Imho Atalas are the #1 or #2 parts bikes on ebay.
It would be best to get a frameset that was sold as a frame - not as a bike - so there is no "right answer" to what components belong on the bike. That avoids obsessive-compulsive behavior down the line in bring the bike back to "stock".
My vote (from my admittedly limited italian bike knowledge) is for ALAN of italy. they got started i think in 1972, and there are lots of these frames around. I just checked and I do not think they have a date embedded in the serial number so the frame would match the dates of every date-marked component you have.
BC at renaissance cycles said a few months ago to me that he was on the verge of scoring some ALAN bonded aluminum frames. however, you'd want an early one with the engraved wreaths on the front head tube - not a later one with no engravings and/or an oval top tube. An added benefit of these frames is that you can take off the stickers and have a period correct (anodized) bike - no paint touchup or restoration required. My bike says "ALAN" engraved on the front lower head lug and "BREV. ALAN OF ITALY" on the bottom bracket, where the serial number is located. My bike came with a mutt-group, not a single component on that bike matches another one, and several don't even match themselves - little bits and pieces are from other products !
- Don Gillies
San Diego, CA