auto or stick just comes to preferance, you lose low 1st gear with an auto, but you also dont have to play with the clutch. like bigarms said, go with the 4.3 vortec if you go v6. the 4.3 is cheap to build to (just about as cheap as building a 350), simple, reliable, and good on fuel economy for a v6. if you go with a 4.3, try to get one from the early 90's or newer, gm had worked out all the big problems by then. if you go with the v6 you wont have to worry about possible drivetrain problems sticking with your 4cyl drivetrain except for maybe the tranny (i dunno how much it can take). if you went with gm drivetrain completely, a gm 10 bolt is roughly the same strength of the toyota solid axle (and is identical to the dana 44), so running a v6 and 36" tires should be about the limit when locked and being bashed, you could push it though (hubs and axle shafts are dirt cheap, 100 bucks for a complete front axle from hub to hub and their everywhere). manual tranny's that i listed earlier, or auto a 700r4/4l60/4l60e (basicly the same tranny, just mild upgrades and the 4l60e is electronically controlled) will work wonderfully behind a v6. a crawlbox from marlin will bolt up behind any of these tranny's according to their site. great t-case to go behind this combo, toyota 4cyl gear driven case, dana 300, atlas (overkill), and np205. the np208 and np241 are good solid cases with 2.6:1 and 2.72:1 low range, but they are chain driven and that can be a problem. you can go with tbi on the 4.3, its available from 86-mid 90's and is simple/reliable


if you stick with toyota the 2.7 is a fantastic motor, good power and good fuel economy plus its a toyota 4cyl.