Probably any 96-98s. The 94-95s were known to blow headgaskets and overheat. 98s are hard to get long tube headers on, expecially if you need emmisions because you need O2 extenders and some other work arounds with the EGR, but it can be done. They all have the same amount of hp up until 99. I would say 97, but if you go with a turbo, then you wont care about LTs so then you could go 98. As far as the split/single port debate, a good set of ported single ports will flow as good as split ports, ported even. When you are ramming air in, it doesn't matter about the intake runners any more, just how well do they and the heads flow. But any V6 > 93 2.3 NA and you wont get the "JUST DO A TURBO SWAP!" in this forum, because there is none (supercoupe, but you can just get pieces and bolt the M90 up to the 96-98s with a good tune and fuel upgrades). Many things can be done with a built V6, just gotta know where you want to go and know it's going to cost, and it's going to take time.