66 Corvette casting number ?

[68l30]

I have a friend looking at a very early 66 327-300 vette with a 3782870 casting. Sorry I did not get the casting date , still working on that one. The VIN is 1009xx with a sept 15 build. Is this casting even remotely possible? The front pad was decked in 76 and a rebuild tag is affixed to the block showing a .040 bore and .010 /.010 on the crank.....no numbers or suffix are evident. The manifold is dated h25 and has the right casting, still need the dist and carb numbers. My buddy was ready to purchase, this may make or break the deal.... Esp at the price point. They are asking 50K , Mosport w/ green gut. KO wheels and AC.......any help or insight much appreciated.

Thanks

BIG