Nice looking rifle. Stock is almost certainly Birch with some factory enhancements to give it the appearance of figured Walnut.
Birch was used on the Glenfield and Box Store editions of the Marlin 80 & 81.
Could be a figured piece of stock wood taken from a Glenfield. In that case it could be Birch.
The giveaway would be the lack of the Marlin 'Bullseye' black&white dot in the toe-line of the butt.
Marlin didn't put those plastic inserts into any of the stocks except the AmWalnut wood stocks meant to go on the Marlin marked guns.
Another would be the butt plate. The Marlin marked gun (like the 81 would have a 'Marlin' logo butt plate. The others like a Glenfield or other storebrands would have their own marked plate. A few just a plain grooved plate.
Marlin never 'enhanced' the wood that I know of during production. Too much time involved .
There was a spray coating of stain on some. The finish itself sometimes contained a color 'toner' to do just that to the wood if it was too light in color for specs.
The latter was mostly on the Glenfield and Box Store guns that were given stocks made of Beech, Birch and sometimes Sycamore..
Light colored woods , much cheaper to buy than AmWal but more than strong enough for the jobs. Plus sometimes they too could have some nice figure especially the Birch.
I don't recall them ever using Maple, but if they did there would be some really spectacular figured stocks around.
The only 'heat' used that I saw used in the wood room was that in an induction set up to burn in the final fit of the Lever Action frames to their butt stocks. Made for a perfect fit.
Very fast , only a few seconds to do each, and efficient. It left no hint of the operation on the outside stock surfaces that the owner sees. Just a slight darkened and glossy hard wood surface to the inletted surfaces inside where wood to metal fit was affected.
