The block stays full after I shut the water.
Agree with Duke........This doesn't sound right and could be a clue. With stats and poppet still closed, It should still be able to **** out not only those out those drain holes BUT!! And mainly, also out the bottom side of the both heads through two specific channels, each goes back into the block (under lower two cylinders each side) then into the drops into adapter plate channels, then into the exhaust box and out the center of the prop.........
On the muffs, you should have water coming out the prop the sec you turn on the hose on, this is the main path mentioned above (don't need stats open or poppet open to have this flow).......Also if it's like mine, not sure they're all the same with respect to these but, I also have two little water jets are peeing out by on each side, just above the cav plate the sec the hose is turned on. These are two of the several drains that allow the block, when combining with the flow out the prop hub center, empty's the engine COMPLETELY of water when off.
If you'r not draining out completely, those paths are plugged......