The 261 engine we assembled for John's big pickup had an 848 head on it. I degreed the cam (a brand new Elgin 261/Corvette) and had no piston/valve interference at all. If you're concerned about things, do a temporary assembly without a head gasket, and as the piston approaches the top of the block at the end of the exhaust stroke, start pushing the intake valve down against the top of the piston and measuring how far it has to travel before contacting the piston. If you can make a full cycle without getting any piston/valve contact, the thickness of the head gasket will be your safety margin. That's how we did it on small block race engines to see how deep we needed to cut the eyebrows in the pistons. On one memorable roller cam engine with 1.6:1 ratio rocker arms, the valve reliefs and what was left of the piston dome computed out to be the equivalent of a flat-top piston!
That engine IDLED at 2500 RPM- - - -slow it down to 2000 and it didn't lope or run rough, it just quit running. We couldn't make a dyno pull at any speed below 3,000, but from 3K to 7K RPM it pulled like a freight train!
Jerry
