i was running 700c X 38mm CONTI Cross-somethingorothers in a TREK 420. It's about a 26lb bike, so not light by aluminum / carbon standards of today. But not ghastly either. Fine for me.
Not a single speed in the photo, but you get the idea of taking a bike for 27in wheels to 700c. My limit here is the chainstays. the little tire hairs abraded the paint ~ only a mm of clearance to the chainstays.
I have an old NISHIKI where the clearance issue is the brake bridge, it's closer than this bike. Possibly it might get the single speed treatment with a a coaster brake, then no more brake clearance issue!

But first I'm going to try a Schwinn Super LeTour 12.2 ('74) single speed build. I am suspecting it will be nearly the same as the TREK, but there's only n+1 way to find out!!




TREK 420 with 700c X 38mm Tires