I understand the innerds of the early and late calipers are different, but are they calipers as a whole interchangeable on my 74? If so, is one more desirable?

Bolt right on

I thought you had to use early caliper with early rotor.
Something with the off set being 1/8 inch different

That's fronts... and it's more than 1/8"

Works , did it.

If real early it may not look exactly the same.

Ah, I didn't read the title all the way.

Yup bolt right up.