As mentioned, easiest, fastest, cheapest and most reliable is to swap in engine with power-output you want. Engine tech had improved tremendously since early-'80s and you're not gonna be able to out-do Toyota's engineering. 1UZ-FE can be found anywhere for $500 or less and comes in 260-300hp variations. Also save you some weight over 5M and makes car even faster!
Here's one in '85 Celica.
Here's one in '85 Celica.