There are a few high-grade traditional-look big game rifles built on the 602 (and the CZ550 BTW) kicking around Australia's Top End for use on buffalo.
True, it takes a bit of skilled work to get them looking "vintage" but the results can be worth the extra effort.

Sorry I can't help with action lengths on the others you are interested in, but someone here will know.

Sounds like a great project. Please keep us updated when you get started.