turbo and electronic boost controller

[subalicious]

hey there i drive a 1989 subaru legacy with such mods as a front mounted intercooler,sti computer,2.5inch pipe exhaust straight through to a 4inch exhaust tip lowered on king springs and sitting on 18inch mags my question is what turbo upgrade would b ideal for my with ot changing anything that i have listed and everything else being standard and what sort of boost controller should i b using