IMHO the whole point of AE86 is being light and nimble. I would stick with anything NA and around 200hp mark. 7A(1.8) block + GE head is popular in Japan if you like to stick with the roots, Toyota but drop in(ish) and powerful 3S-GE Out of altezza RS200 or K20/24, F20C from Honda if you fancy a project and not bothered with having a different manufacturer's engine in the car.
I wouldn't bother with SR20 TBH , DET will be too heavy(and only 200 hp in stock form), DE is only 165HP.
However obviously it's your car and you can do whatever you want...