pipe popping

If it was in my shop and I had not found the "smoking gun" yet I'd pull the head even if Reher Morrison built it. I will add that exhaust popping is from oxygen and unburnt fuel getting into the headers. Either from a weak cylinder (i.e. weak ignition, poor rings, burnt/hanging/bad valve, or a gasket leak. Your cylinder pressure is good but it does nto tell you that much other than the cylinder is sealed well enough to spike the gage. The leakdown is more than likely a bad gage or not enough volume/pressure in the compressor. I own the Moroso and if there's not 110psi or more it can be inaccurate. If the pop isn't bad at idle but gets worse I'd say it's more than likely an exhaust related issue. But you didn't find a bad gasket or header issue and that would have been my #1 thought. If the #7 plug looks like the others on that side then I'd pull the head just to peak. It can't hurt and the cruddy part's already done to get it off.