Why does it have to be a crate motor?
Why not find a correct chevrolet block, and build a radical 383.
You could make it look "exactly stock" on the outside, and only you would know.
Use your manifolds, carb, and all the dressing.
Set your original block aside for when you need it.
That is what I would do.
A real Z/28 deserves a "real" engine.
I hate when I see new engines in old cars.
Just my opinion
