To answer your question, the 88 was available with a 3.0L V6, but a number of them had a headgasket recall that was significant. The wiring hanress should support the sawp, but for the money involved, I'd had another direction. The newer engines, the 2.7L I4 and the 3.4LV6 would be a serious hassle as you'd need the wiring harness and computer from the donor vehicle, not really worth the effort.
chevy small blocks can fit, but require an auto tranny if you have any power at all, as the V8 will smoke the manual, specifically 2nd gear will get killed. It can't handle the torque. You can however swap in a 4.3L Vortek V6, which is a powerful 6.
The 22RE I4 can be pepped up a bit, to around 130-140 hp, and still remain reliable. If you got a carb model, you can exceed that at the cost of reliability.
BTW, Toyota won't swap out any of these engines, aside from MAYBE the 3.0L Toy engine, since the wiring harness is there.
Whay are you wanting to swap engines anyway? Is your 4 dying? Mine has 147,000 and runs like a top, starts with just a bump of the key. If you have no power, did you put on bigger tires? Is so, a gear swap is in order, and will put you back to the power range you're supposed to have.