MGOOF : Modern groupset on old frame

Anything that doesn't flare out under the area for the stem to clamp; if it goes straight down or narrows, you can put a spacer or two in there, and the transition down to the headset will be smoother.

This setup was pretty ridiculous and hacky, but hopefully gives an idea of what things could look like :https://www.instagram.com/p/BZZCnROHen9/?taken-by=the_._meat

The stem was steel, so an aluminum 1 1/8 one would probably be about the same external diameter.