Perry I wish I had the tools at home to do my own valve grind. When I was in high school I took two years of diesel mechanics as a transfer student to the local college...learned a ton. Got to use their equipment and the teacher let us build a few race engines with three angle valve grinds. Unfortunately I will have to send the heads out for a valve grind, and to have the heads surfaced to clean up the mating surface. I'll also have the guides checked.
I think you would be happy with the stock heads. I know another Pantera owner with a 408 with 4V heads that had some "minor pocket porting" done, he dyno'd it and is making 590 hp at 6200 rpm. If they will flow that well for a 408, they should do great for a 351+.