Sorry but I have to suggest that you stay away from the 2.8L's.  I used to have one in an old Firdbird I had growing up and they have severe issues with oil lubrication, not to mention a whole host of other issues.  The 3.1L was built to replace that problematic motor, which was finally replaced by the 3.4L.  As for performance parts, you will find way more for the 90 degree engines vs the 60 degree ones.  The 4.3L is essentially a 350 shortened, so pretty much anything that bolts to a 350, bolts to a 4.3L. ÂÂ
4.3Ls are:
a solid engine
lots of aftermarket support
various fuel systems (carb, TBI, TPI, CPI, CSFI)
90 degree pattern so lots of tranny options (the 60 degrees will limit you to that option)
Stay away from the V8's though.  I run an LT1 in my Ram Air now and without a solid tranny behind it, you're asking for trouble.  Mine has the T-56 manual 6 speed but to put that in a Zuk, well, it's too long, and very expensive.  The only other manual I would ever consider using behind the LT1 would be the NV4500, which is just as expensive and weighs in at a whopping 200 lbs!  Yes, cast iron case, and good luck finding one  :-/  If you go with the LS1, the problems are compounded as those are even more powerful.  Go the automatic tranny route and that's a different story.
Do yourself a favour and if you have to go big, go as far as the 4.3L.  In the end, you'll be happier and have a much more reasonable vehicle than the V8's.  I'm doing the 4.3L now in my Samurai, and I wouldn't do it again.  Too much $$$ and too much time wasted.  Oh well, live and learn.
Cheers,
Steve