Should pretty much be a one-size-fits-all sort of affair, for the most part. I'm of the weird minority that believes multi-piece H's and X's are the way to go, since they're far easier to install/adjust, but some folks will insist on the old-school one-piece units - fine and dandy by me if they're built right, but I've heard far too many of 'em come shipped weird so that a lot of bending/banging/cussing/modding is needed to make the suckers fit on there at all.
MAC has a multi-piece unit with ball-and-socket type flanges on the downpipes connecting to the H crossover - something like that would be my recommendation. My Jeg's X-pipe has a similar concept, except it just uses slip-and-clamp fittings instead of the nicer ball-and-socket deal (and, because of that cheaper design and the ultra-cheap clamps it came with, it leaks like mad ... grrrrr).
Whatever you get, just make darned sure your H-pipe has tranny crossmember hangers on it. It's usually the X-pipes that sometimes don't come with the hangers - yeah, it's easier to install, but the darned thing sags and drags in about a week - but I'd imagine some H's might not have them, either. You might be able to cheat and get away with having one hanger, but I wouldn't recommend lopping one or both of 'em off just to make the bolt-up process easier.