You know its a crate engine, so its not original in that respect.
The warranty crate engines have their own serial numbers that, IIRC are irrelevant to the year.
If you had documentation for the replacement engine, serial numbers and all, I would say yes. Otherwise I would think not. Regardless, I
wouldn't go on an engine block hunt. (unless your
only trying to make money off the car...
)
Here are some interesting sites.
http://home.kc.rr.com/slcomm/vin.htm I always make up a
sequential #, just because I am paranoid.
http://www.chevellestuff.com/1970/index.htm