CobraV8 Simon it looks like you hydro locked the lifters and got contact on the intake valves. All the marks are new??? As far as the exhaust valves, they are smaller and where clearing inside the piston cuts. Unless you have anti pump up lifters you will have this problem again with a 6,300 rpm range. Fly cut the piston tops is the only way to fix this. I don't know what method you use to adjust lifters. I run hydro roller lifters with a .015"-.017" plunger setup. I also have a 65-80 psi
oil pressure system. My lifters pump up at about 5,700 rpms. I do goto 6,200 rpm max. There is no damage from the lifter because of the clearance differents. If you turn down adjusters to spec, 1 -1.5 turns after contact, This is what cause the damage. At lower rpms, the
oil is bleeding out of the lifters to stop valve to piston contact. You said you degreed the camshaft. Some timing chain setups have advance or retard built into them. Edelbrock likes their own parts used as a whole from heads,intake,camshaft,lifters, timingchain kit, and distributor gear. BECAREFUL with running a polygear. It needs good lube between the camshaft gear and itself for cooling as well and lubing gear contact area. Setup of the distributor end play also needed. Check camshaft end play too. I think you will find that the damage depth on the pistons is about .020-.030". This would be about the correct distance the plunger in the lifter would be between normal running and pump up. Rick L. They sell a piston cutter for doing this with a drill. Google it or check Jeg's or Summit. I think they both can get of carry this tool. Rick L.