rebuilt the starter,put in new ignition,new battery,electric fuel pump,coil checks good,plug lines are in order,points are not exact(universal)couldn't get the gauge in properly had to eye it, put new spark plugs in,compresure checked it,1 and 7 are below standards. Spitting up thru the carburator, won't load up. Before I pull the heads off, any other trouble shooting I can do??

when gas comes up through the intake isnt it something with bad timing like maybe a timing chain isnt working?valves are stuck open?i am not sure but that happened on my impala and that is what it was

Your post says "rebuilding a nailhead". Have you had it apart and redone it all or have you only done the accessories? If you had it appart and redid the combustion chambers you should have good compression. Are the valves too tight?

never took it apart, just put the accesaries on. The guy I purchased it from said it was re-done? It is hard to turn, feels tight. I was referring to having to rebuild it if I had no other trouble shooting to perform. Beginning with taking the heads off. Something I don't want to do. Being in the military, my time is getting short. Any suggestions would be appreciated.

Check this out: http://www.aaca.org/ubbthreads/showflat.php?Cat=&Board=UBB2&Number=124428&page=0&view=collapsed&sb=5&o=&fpart=1

Assuming it has never been run, and you have purchased somebody else's rebuild...

IF the job was good, it should be within a 10 pound range from the highest to lowest cylinder. Something that could effect this is incorrect valve adjustment, something worth checking before ripping it apart. Another thing that could give the backfire effect is the timing. To static time the engine, bring it to the firing position on the timing marks and use an ohm meter across the points to determine when the are opening on number one cylinder. Spark starts when the points open.