Anyone have any experience or knowledge of how well these stocks hold up / look / fit on the big guns?

Good by me on a 500a2.
They do have very short LOP.
Look good except for the two slip-on pads,
Leather Pachmayr over Limbsaver. Comfy.

I have the American Safari 458 Lott and it weights 10 lbs, has a Laminated stock.

I wouldn't trade this stock for anything. The weight helps with the recoil.

Clarification:
I thought this thread was about Ruger No.1 ("#1" in title).

Yes, the B&C stock works on Ruger No. 1 chambered for 500 A-Square. I like it.
Should be fine on a Ruger No. 1 in .458 Lott, if you get your LOP correct ... spacer, slip-on pad, 2 slip-ons, etc. ...

I have laminate, walnut, and B&C synthetic stocks for the Ruger No. 1, and have had no trouble with any of them so far. Pretty amzing, considering the recoil levels they have been subjected to.

I fitted the two-piece B&C stock to the Ruger No. 1, myself. The fit on the butt seemed perfect, regarding metal-to-synthetic fit.
I had to file/scrape/sand/enlarge the barrel channel of the forearm to fit the 500 A-Square barrel, which is 1" diameter at the 27" muzzle and a straight taper from a 6" long cylindrical 1.200" diameter shank. Worked fine.

If you get into B&C stocks for CZ 550 Magnum, with full aluminum bedding block in the "Kevlar" model:
It simply does not get any better than that, for stocking a rifle.

You are correct:

Ruger #1