[68post]

The cyl heads were not the problem with TBI engines, the tiny cam and restrictive exhaust were/are.
My $.02 ; a very VERY small cam (single pattern)that's above the original 187*intake duration @ .050 factory cam, K&N filter, and preferably headers with an H-pipe and free flow exhaust. The factory cold-air intake system isn't a problem - but the restrictive paper filter is.
Headers can actually add an approx 25 to 45 ft lbs of torque in the mid-range, (long tube ONLY).

EDIT : reset ignition timing to a custom curve to suit your driving/load/octane.

May not be big gains but you've limited yourself in choices !