The problem with going above .520 lift on stock 496's is not just the clearances, its the fact that the stock springs are weakies. They have just 90lbs on the seat and about 260lbs open pressure. The stock big heavy valves have a tendency to start the lifters into pump up around 4900 to 5000 rpms and if you have any more than .520 lift on stock springs no matter how you get it, cam or rocker ratio you can start to see valve float and lifter pump up (solid lifter) and you will probably have an intake valve kiss a hypereutectic piston, bend over its gone! The stock 496 valve covers are 3/4" approx. shorter (lower) than the gen 6 covers and hence there's less clearance for roller rockers and the poly lock adjustment nuts needed to adjust the rockers. The rocker studs in 496's have a metric adjustment nut and thread and after market kits come with SAE threads, won't work. Wan't to know how we did it, buy our cylinder heads and rockers and you will know.
Everybody loves to tinker and try and make improvements, just be careful you check your tinkering carefully before you put the hammer down! If you have a problem, call us we have complete motors ready to go.
We also have our stainless coil remount brackets in stock that mount the coils under the exhaust manifolds. And our new valve covers with polished stainless tops should be ready shortly. More "Bling" for the 496!
Good Luck with the tinkering!
Ray @ Raylar