Finally got to the garage today. Ended up doing more cleanup than car work. Part of the cleanup was long overdue turn the crank of the spare engine and check it out in some more detail. Shot some T-9 in the spark plug holes for good measure. Looks like it may have been a '68 block, although the -6 suggested to me it was a later casting. I'll have to do some web searching.
One bit of bad news, photo of the stamped number may have revealed a crack in the head.
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