A complete 3.4 swap over a weekend may be just a tad ambitious! But if you do you're looking for a motor out of a '93-'95 Camaro or Firebird.

Note that if you can find a 4WD Rodeo or P'up with GM 3.1 V6 that's a bolt-in with no mods at all.

Another possibility would be a FWD GM minivan, some of the early 90's models came with a 3.1 that had cast-iron heads and a TBI intake, same as your 2.8. That motor had the same block as your 2.8, the larger displacement comes from a 'stroker' crankshaft (same one is in the 3.4) and revised pistons. You may have better luck finding one of those than any of the 'Zu's.

HTH and if you'd like the swap info send a Private Mssg with your e-mail address and I'll forward to you.

Have a nice weekend!............ed