Dave, do you have access to any speciality tools? The best way that I've found to check P to V clearance (after the heads are already on) is to find the point in the camshaft timing events where the valve is going to be closest to the piston. (This is the fuzzy area that Capri mentioned) The intake valve will actually chase the piston down somewhat, and without knowing the timing events of your cam I cant determine where the closest point will be. If you are able to determine this point, put a dial indicator on the retainer and measure the distance it travels when you push down on the valve. This is where the special tool comes in if you are using some real springs. It will hook on to the poly lock on the rockerarm for a pivot point, giving you lots of leverage on the retainer.
Or you could just pull them back off and clay them!
Obviously you havent fired it up, so the gaskets should be ok to reuse.
andy