Marlin Owners indeed has a very intensive site reguarding the repair of these classics.
The model 97 was an extension of the Model 1897...they quit using the 1897 stamp and switched to the '97 stamp in 1905.
The '97 continued on until 1922.
The barrel could be a 16, 24, or 26 incher.
The mag tube could be a half or full length tube...half held 16/12/10, full held 25 short/20long/18LR's.
Value, if restored properly, will go up. A bad resto-job will pretty much leave the value where its at.
As it sits, its a bit of a disaster...but that can be repaired.
I belong to the "If it ain't worth over a grand as it sits, it can be carefully restored & enjoyed" crowd...
then, enjoy using the heck out of it!!
Not many folks have ever seen a '97 up close, and it would be fun making new friends at the local range!
Selling the original sight peep sight would be a mistake, in my view...too useful...as in, way more useful than the cost would show.
The '97 more or less is the same as a Model 39...the 39 & 39A coming later...with some improvements.
A model 39-M (Mountie) stock from Numrich will work after some minor hand-fitting, if you are going for shootability.
If you want an OEM stock for restoration...Bob's Gun Shop is the place to go. He carries old 97 stocks.
ALL are MARLIN GUN STOCKS AND FORENDS , Bob's Gun Shop.Marlin Gun Stocks in Walnut and Synthetic Stocks. Marlin Semi Finish Gun Stocks, Marlin Rifle Forends, Marlin Lever Action Stocks and Froends, Marlin Antique Stocks and Forends, Marlin Synthetic
I can't say enough good about having the gun professionally refinished. It'd cost more, but it'd also make the gun worth more.
Also tends to last longer...but then, a properly done cold blue/brown can last quite awhile as well...
Being that it was your grandfather's, you will feel bad later if you auction it off/sell it.
Believe me on that, especially if you two had a good relationship.
Now...if you are totally committed to spending as little as possible and doing as much as you can yourself...that's cool!
Boyd's straight stock replacement for Marlin is only $42...yes it sez 336, but its basically the same.
Minor hand-fitting needed, but it truly is Minor fitment.
MARLIN 336 STRAIGHT GRIP STOCK
Birchwood-Casey's Cold Blue kit...is ok...I've enjoyed the benefits of using the kit blue, and using their Plum Brown on older antique guns.
The kit comes with all the important cleaning items & instructions...so grab one of those from a local sporting goods store...
then order in the Plum Brown 5oz bottle from Midway USA or Brownells if the store doesn't stock it.
The Plum Brown will give a more appropriate finish for the age of your rifle.
I cannot say enough about PREP work prior to using a cold blue/brown...
Be a little OCD about it, it helps. Clean, Clean, Clean. Polish, Polish, Polish.
Repeat, Repeat, Repeat. Then blue/brown.
Keep the rifle in a WARM room when blueing...the temp of the rifle must stay above 80 degrees, preferably higher.
If you can oven-bake it after applying the blue/brown then slathering it in Cosmoline, so much the better.
Be Warned, your wife will kick your butt if you use the house oven...it will STINK. Get a cheap used oven for the garrage if you can swing it.
After completion, leave it in Cosmoline for a few weeks/months if possible...it'll deepen the Blue/Brown finish.
Heck, its almost wintertime in yankee territory anyway, might as well let it soak for the winter
Ok, the tube mag...as you may or may not already be aware, some of those had a little Button...total pain.
If the button is broken, there are no replacements, unless you get extremely lucky on the auction sites.
You may replace the tube mag assembly with one from a Mountie or any other tube assembly of the same length.
But, before all that, if its working fine, just clean it & slap it back on. Stick a new spring in there if needed.
Run a shotgun .410 brass brush in there a few dozen times, swab it, oil it, and enjoy
The Guts, as mentioned before...Marlin Owners has all the details, & RFC is a good secondary source.
I own a 1913 Marlin model 37 slide-action...between them & Rimfire Central, they'll get you on track.
Oh, one other thing...once you get it back together, you'll want to stick with Standard Velocity (Target) .22LR rounds,
no High or Hyper rounds...its an old gun, and the ammo for which it was made for back then was considerably weaker.
Plus you have to figure in Metal Fatigue over a century...so Standard will be Safe.
With the High V/Hyper V..you risk things that are expensive to replace breaking.
Shorts & Longs should be no problem at all...IF you can find 'em
Hope that helps