Any head off a US spec 603 will fit. .96 and .97 heads use different prechambers and injectors. .96 prechambers can be modified to fit a .97 head. Makes no sense to adapt .97 prechambers to the less reliable older head so I don't know if it's possible. You cannot fit a .96 injector in a .97 prechamber, nor a .97 injector in a .96 prechamber. You should be able to use either pump with either set of injectors.

Never heard of a 603.950 in the US. If that engine doesn't have a turbo, I wouldn't use it in a turbo application. I know nothing about the .962, .963 and .972. There's also a 603.970 in the US = 90-91 350SD/L.

Sixto
87 300D