Yeah, that's a fairly common concern. Most aftermarket stuff is designed to fit into a specific kit. On several occasions, I've been able to take something for one kit and apply it to another. Most times this takes patience, and nothing more, in order to cut, sand or trim something to fit.
Right now I have a True Details 48th P-51 Cockpit set designed for the Tamiya kit which I've managed to incorporate into a Hasegawa kit. In this case, however, I did alotta cutting to get stuff to fit and used components rather than the full pieces. It was definately not a case of simply dropping in some resin, I had to cut the sidewalls apart and do alotta trimming to get them in there.
Sometimes this is the case even with a kit for which the resin was designed to fit!
If you play around enuff, you'll eventually get things the way you want them. Don't be afraid to jump in. I used to analyze everything and never got anything done. Now I "just do it"! LOL
Fade to Black...