M91s are the toughest rifles to take down w/out scratching up the stock.
The barrel bands are threaded in a way that opens them up as you turn the screw clockwise. Even then sliding them off often results in scratching the stock. Luckily some of the 1/3 Finn mix rubbed in will hide any scratches you may make.
PM me the night before the shoot and I'll bring you some if you don't have any. I made a tub a year or so ago.
My advice would be to use some Kroil and let it soak for a few days. Don't soak it, just a few drops on each side should do it.
As for the handguard, once you get it off just use some acetone or mineral spirits to clean it really well inside. Open the crack with a little pressure and use a Q tip to get any grease, oil, or dirt out of there. Once its clean and dries for a little while, take some Duro Super Glue gel and run a bead thelegth of the crack while again seperating the wood. Then let it close and give it a quick wipe inside and out with a rag lightly dampened with either mineral spirits or acetone to get any excess off. Let it dry over night before putting it back on and your good to go.
I swear about 1/2 of the Finn rifles out there have cacked handguards. You'll barely see it though afterwards as long as theres no wood missing.
BTW... watch for any pins or tiny screws that may be hiding in front of the bands. The Finns often sunk these in to keep the bands from sliding forward.