You'll be stripping many of the components from the junkyard engine and using components from your 76 engine. But the guts of the engine should work okay.
I don't believe there is any difference in the block and cyl head size than that which if found on a 76.
Get a guarantee on the engine. And be sure you can check out the engine before the warranty period expires.
Actually, $450 sounds a little high from a JY unless it does come with a solid guarantee.
don't know what to tell you about your transmission. I will assume it will work okay.
