Would the HVA be considered a Mauser? Updated M96 with M98 length and third lug, but still small ring.
Mine came in the form of a JC Higgins 51L 308 that was some beat up. Recoil mortise block had busted loose from the stock and the tang was split. Bought it for a donor, but used accraglass and pins to replace the wood block and glass the action. Shoots too good to change now. Currently using it as a cast bullet platform.

I would say it is.

Yes, although with a few slight modifications. The ejector/bolt stop and safety being the main ones. The aluminum bottom metal on most of them is also different but FN steel bottom metal fits well.
But they are very good actions

Not a thing wrong with those.
Very well built.

I need to pick up another one to build a 7X57 or 257 Roberts someday. I'm liking this one too much to tear it down yet.

What version Stock do I need to fit the HVA in 7 Mag?

My SIL has one of those rifles. It belonged to his late father. It needed bedding and a few small cracks fixed. After he got that done, it was one good shooter.