"Bent freehub"?? There is some play to the freehub body (and freewheels) but not so much that it will affect normal shifting operation.

I've seen a HG cassette wobble badly once, but that was caused by missing spacer shims.

I can't see any reason to swap out the 600 drivetrain unless it's damaged or very worn.

You sound nearby to me. PM me if you wish to stop by for a 2nd opinion. I have two Uniglide rear wheels (105 and 600) so I have some experience with their assemblage.
I can also install a new chain for you while we're at it. You can pick up a compatible 6-8 spd chain at Walmart for $8.