The size of the turbo will dictate the amount of mods you'll have to do. A small turbo like a TE-44 or TA-49 will need atleast 36 lb injectors and a chip to compliment it. Other than a gasket for the drain pipe, and perhaps a passenger side breather, that *should* be all you need. Any turbo bigger than those and you'll most likely need to get a high stall converter, otherwise you might be facing spool up problems. I'm sure others will chime in as to what else you'll need.
