3S-GTE in rolla 86 - Bad move, I'd say!
Everything is possible, people have put 3S-GTE in Starlets but traction even with LSD is a major issue and the mileage you get is somewhere between 8-10kmpl.
I've used 4E-FTE in AE101 Rolla and I used to get 16-17kmpl in city with a light foot and a bit of boosting (you can't help it) and about 12-14kmph with a very heavy foot (every shift with boost).
I'd agree with Immad, that 3S-GTE for 86 Rolla is an overkill.
If you find a clean 4E-FTE motor it'd be the best decision, upgrade the turbo, FMIC, etc. It should be enough for you, unless you're into drags, etc.
Cheers