I'll let the true gunsmiths answer the rechambering question.
As to action length, etc, a 6mm Rem works fine in a short action.
I had an early-ish Varmint Special in 6mm, it was built on a short action, and shot absolutely great.
Sold it (
), missed it, and had another one built, again on a short action.
Recently bought a 40-X in 6mm Rem, on you guessed it, a short action.
I use mine for groundhogs and paper, so I never even bothered to check for mag length, etc, as they are always single fed. With you mentioning VLD's and A-Max's, I don't know what your intended use is, but that doesn't sound like something that you'll need a magazine full of ammo.
The 6mm Rem is an AWESOME cartridge, and I love mine. However.... if I had a rifle in 243 Win that shot well and still had good barrel life left in it, I'm not sure I'd go through the trouble and expense of rechambering it, "just because".
If on the other hand it's shot out, go ahead and re*barrel* with a fresh tube in 6mm Rem.
You won't regret it!
