Seriously, you will always save $$$ if you buy a modded car off someone else however there is a greater chance of getting a car which has had a hard life.
12A into a KE55 is possible and I doubt it is often done ... the only one I'm aware of is used a the drag racing team which had a V8 supercharger in it & now a 13B ...
You'll be best advised to get suitable brakes + stronger driveline & diff, nothing less than a Hilux diff + either W58 or RX7 series 4/5 gearbox.