Here is a rifle that might pique your interest. This rifle was built by the Stratton Family at Virgin Valley Guns.
It has the following features:

Winchester Model 70 classic Red Box 7mm Mag
Sunny Hill bottom metal (floor plate release inside trigger guard)
Winchester .375 H&H parts inside action
The barrel was made by Virgin Valley Guns
NECG express sights
26” medium weight express barrel in 8mm Remington Magnum
Gentry Custom Barrel band front sling swivel
Laminated stock with rosewood tip and cap
Pachmayr Decelerator pad
Talley scope bases and quick release rings
I haven’t fired the rifle yet. I don’t have ammo, brass or dies. I might send it right off to be rebored in something heavy, such as a .375 H&H or a 404 Jeffery.

So you converted the M70 in 7 Mag to 8mm Mag? Did they cut the front and the back of the action to fit that long cartridge?

Virgin Valley did all the work. I haven't received the gun yet but I'll report on it when I have it next week. As the 8 Mag is based on a full-length .375 case, and M70s have been used for 375s for some time, I'd say that the gun handles the 8 Mag. I don't know how they made it feed. But the gun has been to Africa at least once, so I'll bet it feeds just fine. My dilemma is whether or not to leave it in this caliber or bore it out to something big. In my opinion a .375 or 404 Jeffery wouldn't kick as bad (recoil velocity) as an 8 Mag.

The rifle came in yesterday. I don't have any 8mm Mag ammo, but it feeds .375 H&H ammo just fine, and almost chambers it. The gun weighs 10.5 pounds, so there is no way I'm going to use it for hunting as an 8 Mag. I have a 300 Win that weighs 8.5 pounds for that application. Looking at the action, it appears that the magazine well was opened to the rear to accommodate the long cases. The .375 ammo I tried in it was loaded with 270 grain bullets and they fed well. If I don't sell the gun I'll look into having it rebored to something large that will justify those iron sights and the parade of rear sight leaves.

Depending on barrel contour thickness and ability to thin it out within safety margins. I would measure the contour and contact a barrel maker first for straight answers and piece of mind. If there is enough meat in the barrel the simplest, most practical and sale wise is the .375H&H. The .404 needs the bolt face bored out and could cost more in labor. The .400H&H is a thought. Best of luck to you.

The 8 Mag case is a blown out .375 H&H so reboring to .375 is not an option as the chamber will not clean up. The .416 Remington will only require a rebore and rethroating. The case is the same as the 8 Mag. This is a $350 job with Clearwater reboring. I already have a .416 Ruger so this gun will just go up for sale for someone else's use. It is for sale now on Gunbroker.

Someone might want it as is. The way I see it, it's more of a rebarrel job if a caliber change is desired- Copy the same contour, and save the sights, and band. Price is only a touch more, and a heck of a lot simpler. Then any full lenght belted or beltless cartridge is a possibility.

I sold the rifle to another local southpaw. I ordered a Talley one-piece Picatinny base with 20 degrees of elevation built in. He's going to get a 6.5-20X scope for it and we're going to work up some long range loads for it. He wants to shoot 200 grain bullets for those long shots. It's a good thing he's a big boy at 6'5" and about 280 pounds of muscle. The gun will weight 12-14 pounds before he's finished.