Originally Posted by FBinNY

The key places of frame/component compatibilty are at the bottom bracket, headset, Brake type and position or reach and seat post.

Most likely the BB will fit, but someone might throw you a curve with a 73mm BB,

Headsets used to be easy, all you had to do was make sure one wasn't JIS, but these days even though both are probably for 1-1/8" forks, but these days there are almost as many incompatible headsets as front derailleurs.

Brakes, have to match, ie. disc, canti, or caliper, and the reach of a caliper has to match

We all know how seatposts are all over the board. If they're not both 27.2, who knows.

Then there's other details like tire width/clearance, front derailleur braze, or clamp diameter.

Lastly, depending on changes in geometry, there's a good chance that though the stem cam be moved over, you won't want to.

I listed the most common issues, odds are you'll face one, but you'd have to be awfully unlucky to have 3 or more issues.