I´ve got some experience (7 years) from endurance racing and first of all make sure that pads, fluid and cooling ducts are up for the task of handling the heat.
Since that does not seem to be a problem in your case, the biggest improvement by far, that the team experienced was when we did a proper corner weighting!! We had driven a few races after a major chassi overhaul and braking was all over the place, but after the CW braking efficiency was spot on.
So I´d say, fix you dampers and get lower treadwear tires (if it is allowed?), then get coils and do a proper CW. Could perhaps still do a CW without coilovers by moving weights or stuff around in the car... but could get a bit tedious
Edit: The car discussed above is a BMW M3, not the Datsun... just to clarify