If you had water in the valve area, that is probably not due to a blown head gasket. However, 390 intake manifolds, and their water passages are partially under the valve cover so a blown intake gasket could cause a miss and water in the valve area as well as in the oil.
I would do a dry and wet compression check, the low compression and water may not be related. A leakdown test may tell you more than just compression. Also, if you have access to a cooling system tester you could pressurize the cooling system and look/listen for leaks.
