The 86-88 Turbo II's using a mechanical oil-metering pump for the turbo, which was much more reliable...but the motor's themselves had heavier rotor's with lower compression than the 89-91's...

The 89-91 motors utilized an electrical oil-metering pump, which was was deemed as being less reliable than a mechanical.

On my '88 T2, we ended up having a Series 5 (89-91) block (lighter rotors/higher compression)...while utilizing the Series 4 (86-88) mechanical oil-metering pump for reliability.

It worked beautifully.

SO my point is...and as everyone else will agree....don't waste your time and money trying to turbo the N/A motor. Just purchase a 13BT out of a Turbo II. Keep in mind with your car being an '86 though, if you purchase an 89-91 motorset, there are going to be some wiring differences.