88 t1 motor has lightweight rods and a mitsu turbo.
Manual or auto?
The 255 is a good fuel pump to have. But it's purpose is to supply the fuel the motor needs, it is not necessarily an upgrade that allows for more power with out supporting mods. With the lightweight rods and the mitsu turbo you are really hankered on how much power you can make with the car. I like the mitsu for stoplight to stoplight and street brawling at low speeds but the mitsu turbo is no turbo to use to make power. Over 14 psi its like a high speed hairdryer pushing really hot boost into the motor, kind of counterproductive.
Personally I would keep the car the way it is and build a nice t2 cb motor. Even a stock t2 motor with a garret turbo is going to be worlds different.
Before we start make sure the drivetrain and suspension have a good clean bill of health. Tune up, good compression, minimal cylinder leak down, fluids all nice and clean, good motor mounts, tight front end etc.
But if we are going to work with what you got this is how I would do it with both manual or auto.
I would throw a good boost gauge in it first off. I have ran faze boost gauges with success but a nice autometer unit would be optimal. I would run a FMIC or a t2 rad/ic unit out of a Daytona. FMIC being the better choice but the daytona rad/ic being more of a bolt on option.
The injectors, comp and map need to be upgraded all at once. All 3 are necessary to function correctly. You really can't run any of them without the others. +20's, 3 bar cal and 3 bar map would be fine. A FWd stage 4 is a great computer, no need for a stage 5 with out some top end upgrading. With the stage 4 I would also suggest a wideband a/f gauge and an adjustable fuel pressure regulator. FWD computers run rich and need the fuel pressure to be turned down to make the most power out of them. With the mitsu I wouldn't run anymore then 18 psi. You will notice a power increase but like I said, the mitsu tends to heat boost above the 12 psi mark. A garret t2 would be a cheap upgrade and is good to about 250 hp. Beyond that mark I would start porting the top end and go bigger turbo.
With the auto, I would do the basic upgrades like bigger trans cooler, valvebody mods, turn up the line pressure etc to make sure it will last under power.
The manual should be good to go (a520 in your case) aslong the fluids nice and full and the clutch is good and strong. A t2 disk and t3 pressure plate is always a nice upgrade for a mild street car not putting down a whole lot of power.
Again I can't stress the much a hold down the stock turbo is. they will boost creep with the 3 inch and you should already notice it. I just bout a 2.5 5 speed lebaron and I have to watch 3 gear getting towards the 5k mark because it wants to overboost set at the 13 psi mark.
If you have any more questions feel free to put them up, I have had a whole lot of different cars with different set ups.