My front subframe is cracked so I bought one that was advertised as "95-99 Mitsubishi Eclipse OEM mid car cross member engine cradle support". I haven't taken mine out yet, but after taking a closer look, I am noticing some diferences and someone wrote with grease pencil on the one I bought that it is for a A/T GS Eclipse.
Do the A/T models have a different subframe, or is it 420a that is different?

I believe it’s just the 420a part of it that’s different.

420aTurbo model

The main difference is there aren't any inserts for the rear motor mount

Ahh I see what your talking about now. Lol my bad.

There are differences in the subframes depending on year . That I know for sure and have posted that up somewhere. It didn't affect them being used between years. The new ones had more bracing from the factory. I do not know what if any there is between auto or the gs units however.

My GS and GST differ, from what i know only the versions with the 420A are different front the engine mounting bracket. It wont matter if its AT or M as thats not an issue between the 2, but you need the GST or spyder one as thats the engine side you have and the mounting for the engine is correct.

Also years dont matter, my 95 GS 420A parts car is and has the same metal and bracing as my 97 GST car, i have not checked if clearences are different though but i imagine they should be the same

Early and late AWD subframes are different, the later one has one more bolt each for the triangular stiffening plates, and there's a couple of other subtle changes as well. IIRC the longitudinal member that carries the front engine mount is slightly different as well. I have never looked at non-AWD subframes.