How can I tell if my 88 5sp D/R has LSD?

It says what the ratio is on a tag on the back of the diff. It also will have in big letters - LSD. Thats if you have it.

Look at the lable; if it's lsd, it will say so. Another method is to jack up both rear wheels and put the car on jackstands. Put the car in neutral (engine off of course) and turn one rear wheel in a forward direction. If the other rear turns in the same direction, you have a LSD differential. If it turns in the opposite direction you have a standard open differential.