I was also wondering u said crane cams and u broke a pushrod.
Check your valve train geometry your rockers should never leave the center of the valve stem.Another thing with that broken push rod did your piston smack the valve it may have bent the valve and that also might be the pop u hear if u bent the valve it may not be seating properly. Do a compresion check if u dont get it figured out maybe it will help figure out where to start if u have a valve that s not sealing. Dont junk that 400 i am building one at the moment and i may need ur info