Piston to valve clearance should not be checked at TDC as the clearance will be tighter on ether side of TDC. The last thing you want to check is piston to valve clearance - after you have finished picking the rotating assembly, deck height, head gaskets, valve train you are going to run ( including the correct pushrod length as it will effect clearance ), lash. This is easiest done before the short block is finalized and assembled. Mock up one hole using valve clearance checking springs. Rotate the motor over TDC ( at least 25* on ether side of TDC and measure the piston to valve clearance with a dial indicator off the valve spring retainer every few degrees.
