Pretty bad idea for an SR or CA when they are v.hard work to fit due to sump location, no off the shelf fitting kit for them, and you end up with something pretty average anyhow.
Youd just end up with a slightly lighter car than an S-body with far less sophisticated suspension and less parts available.
Off the shelf engine and box fitting kits for Toyota 1JZ and 2JZ, Nissan VG30, Chevy V6, Ford V8s, Chevy V8s, Mopar V8, LS V8s, Ford Pinto, Ford 2.3 Lima, Ford Cosworth YB, and probably a load more I cant remember, no cutting or welding, just bolt straight in, most of these include suitable radiators and propshafts if you REALLY want to make it easy for yourself.
I'd do one of them unless you fucking badass at fabrication and wanted to make it hard for yourself.