It'd be cool to see a modern 4.8/5.3 swapped in...or even better imo, a 4.3/4l60-e combo with 3.08 rear for ubber mileage and pretty decent performance...
The latter 4.8's at 295hp would be pretty stout.
Ever consider just random, non gm swaps? Toyota 4.0? Jeep 4.0? Jeep 2.4 (150hp) or even later 3.8's (202hp) from the wranglers (rwd configuration). Ford 3.8, 4.0, or 4.2 SOHC v6 could fit the bill too. Mopar 3.7 v6 (210hp) or even 4.7 SOHC (230-310hp) perhaps? All rwd drive available and sure to be found in wrecking yards. Sure, harder than a GM swap, but when has harder ever deterred you?
If you do an off-brand swap, just stay away from the 4.6's/5.4 fords....belch!
Maybe a cummins 4bt?