Ott, unless you're willing to sacrifice a LOT of low end torque and end up with an engine that has a very rough idle and won't run well unless it's wide open, stay away from long duration, high lift cams. The stovebolt cylinder head just won't allow enough airflow to make a lumpy cam worthwhile anyway.
Cam specs written for ".050" cam lift" are worthless for figuring valve to piston clearance. The rocker arm ratio on a stovebolt engine will have the valve open much further than that. You need a degree wheel, a dial indicator, and at least one piston and valve setup assembled and adjusted to monitor the piston and valve position in real time to get an accurate measurement. I use very weak "valve springs" so I can move the valves with thumb pressure while I'm checking cam timing and drawing a lift curve, just enough spring pressure to keep all the parts in contact with each other. As the parts approach "crash and burn" territory, I physically check the clearance with a dial indicator on the valve spring retainer by pushing the head of the valve into contact with the piston. I'd stay far away from a piston with a valve relief in it unless you've dons some radical head milling and/or block decking. On an OEM 235/261 block that hasn't been decked, the piston is about .050" or slightly more below the deck. Unless you've eliminated that fudge factor with your custom pistons, that needs to be taken into account when figuring valve relief cuts, also.
Jerry
