One big thing to consider: if his block has been run (and it certainly looks like it) for thousands of miles already, it's pretty much good to go.
I do remember long ago while at Brigance Chevrolet in Oak Park, IL in the early 70's (confession: started out racing BBC''s in early Camaros!) once in a great while a car would come off the car hauler and the engine leaked oil into the coolant, the other way around or fluids just leaked out period. Chuck White, the expert parts guy, said the mechanics would just do a fast look-over and then pop the engine and stuff in a brand new replacement long block! I asked Chuck why and he said that since the car was new and untitled, they took a risk in doing a teardown and repairing the numbers matching engine. Instead GM said to put the removed engine on the side and await pickup for inspection.
Sad part? Chuck later told me it was b.s. and the GM driver that did the pickup said the engines went right to a junkyard where they were smashed up and recycled. I wanted to buy one Z-28 302 and one BBC from the set-aside pile but this was strictly forbidden as the dealership then would not get credit for the new engine swap!