Specifically 1gb (93-94) front calipers are same as USDM 91-92 GVR4s, 1ga DSMs have single piston front calipers.
Zee,
1G DSMs were built on a shortened chassis of the E3x Galants, so many of their parts eill interchange with the Galants. A DSM rear subframe is the same as the Galant's but without the 4WS components bolted to it. You really don't have to change out the subframe, just to swap diffs.
If you are still running ABS, you will need to swap the ABS rings from the galant hubs onto the DSM hubs, to retain ABS, iirc. There are several how to threads on "5 lug swap".