Buck vs Practicality !! Forget the A15, that needs to be engineered. For half the price of engineering, you can get an A15 internals, throw the balance towards a better box and like D: said stroke it and waiver the engineering. 150 atw's is a big ask and quite achievable with a turbo, but as you said you want a streeter that you can casually drive down the road. And 150 ate would be a more realistic number to hit. I would guess 115 rhp - 120 rhp. That is no slug !! Been turbo, you'd get away with just a H165 as the top race cars run 1303cc and 150 hp with H165 diff (torque kills diffs) and thats more money saved. You should get away with a 60A (approx $800+) box if your nice, more money saved, but celica (approx $1350+) would be safer and practical for 2 reasons in my mind. It can handle abuse much more and been shorter gears, the turbo will kick in quicker. For the extra $$$ over the 60A its good insurance. 150 bhp, keep in mind you said streeter, is a different kettle of fish. Definitely more money on internals and I would say less engine life. And I also think alot less streetable. You will want better brakes and much better suspension to get that power to the ground ( more money). Alot of people forget cause a car with heaps more power and #OOPS#t suspension will get his butt kicked with a similar car with less hp and good suspension.... Now going for a different engine is practical in my eyes if your still demanding a 150 bhp+ streeter, ya mum can drive to the milk bar and back and still get up n go. But much much more money and aggravation. You will have to change all the running gear and engineer. You will get alot more engine life aswell... So in conclusion I'd stick to a more practical A12 stroker turbo and be content with 110 bhp to 120 bhp under budget that will have longer life and is streetable.