I would seriously consider an upgrade to higher ratio rockers. This may mandate a spring upgrade as well. Check the installed height. If it is around 1.8", you can use Chev LS beehive springs. You would have to source retainers to fit your keepers. Beehive springs perform better at controling the valve and spring harmonics/resonant frequencies which can enable valve float. There are millions of LS engines in bone yards to source good springs from for little cost. Spend on what is important, good reliable roller rockers. If considering removing the heads to touch up the valve job going to LS valves can be considered. This would require replacing the guides to fit the 8mm stems, 5/16" bronze guides and hone .001" to .002".The LS valves do not wear much so you could possibly use the valves, springs, retainers and keepers from heads removed at a Pick n Pull yard for not much more than peanuts. Let your machine shop cut new seats as required and touch up the valve seats with a 30° back cut on the intakes. Re machining the exhaust valves and seats for a 40° angle can aid low lift flow when max lift is no more than 0.500". With that in mind you need to grab the low hanging fruit where ever you can. Some bowl work and minor porting to remove casting ridges and gasket match the ports. If cutting a little out to improve flow, consentrate on the cylinder wall sides of the port going past the valve. On the cylinder wall side of the guide the roof of the port can be raised a bit. Narrow the guide and aero shape it. On the cylinder center side, just take the roughness off as the guide is shaped. The port floor is a dead area to speak of, so just remove casting imperfections. Inexpensive valves and some carbide burrs and 80 grit for the diegrinder could get you more than you hope for with high ratio rockers. Still very reliable and drive like it came off the showroom floor.
