i agree 100% with the B18 idea, and if your stuck on this head swap thing do the LS/Vtec personaly i think thereas alot more info on the LS/Vtec and i think its a more strait forward deal compared to the B20. with the B18 LS/Vtec or GSR your going to be able to make more then enough power ith witch ever rout you go, but if your looking to build a B series with the most of everything TQ, HP, LTR's ETC. ETC. then go B20, but thats hard on the wallet and from what i understtand thats not gonna be the best choice for what your trying do.
my vote = B18c1
2nd B18a/b LS/Vtec
though in my mind the B20 is still a very interesting motor B) it just dont seem right inlesss you got a butt load of cash to make it right and get out of it what you were looking for when you bought in the first place.