OP, your post is going to tread on a few toes here. Simply because some folks believe it to be sacrilege to change any milsurp, no matter how common.
I don't particularly recommend it myself, but each to his/her own tastes.
The M91 and M91/30 and a few later platforms are excellent OLD SCHOOL DEVICES. They WORK first time, every time, even when they haven't been maintained regularly.
I don't own one with an aftermarket stock, simply because they don't appeal to me.
I did put one together for a fellow and took it out for a test run to make sure all was well, before turning it over to him.
First off, I had a heck of a time finding a stock in Canada. By the time I got one here from the US, the cost was close to $600.00 Canadian and a 4 month wait. I won't tell you how it got here.
It's pretty easy to fit to the 91/30 and the trigger channel is cut out for an aftermarket trigger. The rifle that went into it was fitted with an SKB instamount, I had on hand for a few years and set up with a Leupold 2.5X long eye relief scope. YES, it did take a bit of fiddling to get it bedded nice and snug.
I have two vintage M91/30 sniper rifles. One has a PU scope and definitely looks like it's been there and done that, still, it will shoot the hand load it likes into just under 2 inches at 100 yds and factory surplus, just under 4 inches. The second rifle is an FTR 91/30 with a PE scope, attached directly to the top of the receiver and IMHO is much more solid and precise than the PU side mount. Both rifles have excellent bores and their barrels carry a serial number matching the scope bases. The PE scoped rifle will shoot its preferred hand load into 1 1/4 moa and less, as long as I do my part.
The rifle that went into the Archangel stock was a 1938 dated Tula. It was still in the grease when it was given to me by its owner for the build.
That adjustable stock was very ergonomically stable and correct for me, once it was adjusted to my taste. The fellow that owned it, is of similar build and hasn't adjusted it since he got it. Yes, he shoots and hunts with it. He's a Russian immigrant and loves anything Mosin Nagant.
I took all three rifles to the range, mostly for fun, but also to see if the new stock would make much difference.
I really liked the handiness of the detachable magazine. However I had a bit of difficulty getting it to feed cartridges properly. They didn't want to tip up enough and jammed. This was fixed before going to the range.
I used a common batch of ammunition, that had proven accurate in both of my snipers and a couple of field grade shooters. 2 inch average groups, off the bench were consistent in all of them.
The Archangel stocked rifle shot it exactly the same. appx 2 inches at 100yds.
The felt recoil was less because of the recoil pad and fit of the stock.
I shot it out to 400 yards and the groups with the surplus Hungarian ammo stayed the same, 2 MOA.
The fellow I sold it to, only uses factory Norma ammunition and he says he's getting the same results with it. He loves the look of it and that's 90% of the appeal for some.
If you like the look and are handy, the stock, if you can find one, isn't a bad choice at all IMHO.