It appears this is an '870' block. The date code is H163 (1963 engine) or H168 (1968 engine). The heads are from 1964. I'm just listed it on Craigslist in the Minneapolis/St Paul area for 'best offer' It it is not gone by Monday it is going to the scrap yard.
Another expensive lesson I have learned is not to buy an 'as is' engine. Shame on me.