I've been acquiring some components for this build in the last couple of weeks. In hand I have: Suntour sprint flip flop wheelset and cogs, challenge paris roubaix sew ups, Campagnolo Gran Sport rear derailleur, GS shifter, Atom 4 speed freewheel 14-22, grease nipples from UK, Brooks swift saddle, and record pedals. Patiently waiting for: GB spearpoint stem with Reynolds alloy Bailey bars, Reynolds R5 alloy seatpost, GB standard brakes hiduminium, cheap headset, shimano un55 cartridge bb.
My persistence to use Campy record bb and headset did not pan out well. Neither worked. BB was super tight on drive side, I didn't even try non drive. Headset race was too small and stack height looked too high. I bought a cheap 1" threaded headset with a larger fork crown race 27mm for now and a shimano bb just to get things rolling and make sure I have all the right sizes before investing in something period correct.