Better off putting in a 4G63T from an Evo, than you would from a GS-T/GSX. But if you're dead set in using a motor from a GS-T/GSX, then like Turborx8 said, you're better off selling the RS and picking up a GS-T or GSX.

It's not worth the trouble to do a swap, and if you're wanting to make some real power, I personally wouldn't bother, trying to turbo a 420A. There's a lot of info on the net, regarding this topic. If you have any aspiration of wanting to turbo your RS motor, then this group of people can help you out: 2GNT.com

Also check out VFAQ Site - Visual Frequently Answered Questions for a lot of good DSM info.