Texas,
I did the same conversion from a Win70 Classic Sporter (CRF) in 300Win Mag to 375 Ruger. The conversion was done by a gunsmith who posts on here as Redneck. The only feeding issue was the cartridge on the left side of the magazine would occasionally pop out on its own. The fix was to open up the top of the mag box where it angles in. That allowed the more bite from the feed rails. It fed perfect after that little tweak. There might've been more too it and if you want more info, just send a PM to Redneck.
The build ended up being 9 pounds, 2 ounces with Leupy DD mounts/ring, VXIII 1.75-6E and 3 rounds. Recoil was very tolerable for me especially with a 1" Pach Decelerator on the stock. If I was building another one, that would be my target weight. I only used Hornady's 270 SPRP and RL15. I got good MOA groups no matter the charge weight just an steady increase in MV.
A couple of things to know about my build and the 375 Ruger in general. Without modifying the mag spring, only 2 cartridges fit into the magazine. Supposedly you can remove the "hump" from the spring which allows a 3rd cart. Another observation on Ruger brass is that it seemed to be very soft. If the case mouth was not chamfered pretty heavily, the flat base of the bullet would slightly collapse the shoulder. It was not big deal but I've never run into that before when loading for a 375H&H.
YMMV but this is my views on the 375Rug and a M70.
RH
