Head gasket removal

Pickup stopped running two blocked from home. After cooling down noticed no water in radiator. Checked dip stick and water was in oil. This is first time into engine so it needed to be right. The block had no cracks and very little if wear inside cylinder walls. We changed head, timing chain and gears, timing cover, water and oil pump, starter, alternator and battery, fuel pump and carburetor. Go this deep into the engine my son wanted to change everything possible. After installing every thing I noticed engine turning to easy. It has very little compression and is blowing back through valves under valve cover. We placed engine at TDC with distributor and cam gear lining up correctly. Not sure at this time what else to check.