Have you flushed the cooling system yet? Perhaps try pushing some air or water back into the drain hole once you can adapt a 1/4" pipe nipple. When I had my motor apart i had it hanging from one end off my engine hoist. I ran water and air into the block back and forth until all the crud stopped coming out and just ran clear. I would guess a couple of pounds of sand and scale came out.

Mark


1952 GMC 9430 one ton pickup, a work in progress

1952 1-ton pictures on Photobucket