For all intents and purposes, 302 heads are pretty much the same as 289 heads. Take yours, buy an air compressor,die grinder, some porting bits, and a port/polish kit, and get to work on the ones you now have. All that's really necessary is to clean up the intake ports, gasket match them, clean up the area under the valves. The exhaust sides need the same, except the ports need to be open up, blended into he bowls, focus on raising the roof and sides of the ports, the floor just needs smoothing and polishing. You should also polish the chambers and unshroud the intake valves somewhat.