what would it really take?

I wouldn't do it, either. While that my be a good deal for a racer (I wouldn't know), It's basically a shell for your purposes, and you'd need another complete parts car to make it right. And no, not all of your '74 interior parts will work, unless you wanted a bastardazation.

It sounds like the '74 is well on it's way to being a good street cruiser. I'd learn on and finish that, and something better suited to your needs will pop in time.