The odds of such low compression across all cylinders being valve or head gasket related is quite low.

You must now do a cylinder leak down test on each cylinder and while each cylinder is pressurized listen for where the air is escaping. If you hear it through the oil filler hole, it is cylinder/ring/piston related. If you hear it through the throttle body, it's intake valve related, or through the tailpipe it is exhaust valve related.

These numbers, assuming that they are given in PSI are quite low. Typically numbers that low will happen in only one or two cylinders.

Continue your analysis and post the results here for comment before tearing it apart. Look before you leap.