Okay you have some date codes there.

First for the heads on the mortec site

3890462 = Camel hump heads, made years 1966 to 1967

For 302, 327, 350 engines.

They are 64 cc closed chamber heads

Casting date D 20 7 cast on 20th April 1967

Block Casting code

8 L 29 = 29th Dec 1968

So this makes it the good solid Heavy american made block, Just hope that your cylinder bores are at .030 " over that would be good .060 " would still be okay but that would be the blocks last bore.

So there you have it a block nearly 40 years old and heads that are practically 40 years old. Old chevy iron, but still good (after checking ) use it like it should be used.