VTEC head swap onto the OEM B20a/B21a is possible but is not very practical. There's not much info so you'd be basically heading into uncharted waters.

H22 swap is doable but the company that made the kits went out of business (Place Racing). You can do custom mounts with custom axles (94-97 Accord inner and mid-beam with the OEM outer joints) and then do the wiring (OBD0 to OBD1 for 3g's that came with a B20ax stock but the B21a1's are OBD1 so you just need to add the vtec wires like doing an H23 to H22 swap (and maybe a few other sensors that weren't on a 3g stock).

Please visit for more H22 swap info:
http://www.teaminterlude.com/3rdgenh22swap.asp
http://www.preludepower.com/forums/s...d.php?t=190047
http://www.honda-tech.com/zerothread?id=1165546

As for doing a GSR swap, it would be a bit harder than the H22 because I've never seen any info on the swap (writeups) such as the axle combination(s). Just a bit harder but then again you'd be lacking torque with the B series (but that's a matter of preference).