Another 3T which would be cheap, but you know how "high performance" they are.
A 3TGTE, easy to do, but you sound lke you don't want to go turbo.
2TG - Twin cam and goes remarkably hard with a screaming top end, although you lose some low down pull compared to the 3T. Can get this fuel injected too. This is a VERY simple swap and would be my recommendation.
Change the crossmember to an AE71 member and bolt in a 4AGE, or 4AGZE. Changing this would involve a bit of messing around, but is pretty simple.