Originally Posted by
CV-6
I think you would be better served running fatter tires, but I am pretty sure you are going to be limited by the frame.
An '84 Trek 760 should handle 28mm wide tires no problem, maybe even 32mm.
What is the seat lug on the OP's bike? If it has the seat stays attached to the sides of the lug, 32mm should be fine. If it has the more modern investment cast "fastback" lug, it might be a little tighter. Measure the width of the stay separation at the tire radius to be sure.