Wish he had pictures of the sling well markings, inside barrel channel and the frt nose of the stock. Having the numbers stamped in slingwell may very well show use by SG.
Stamps look to be correct, but I'd need more time to magnify and compare.
Either way IMHO it's much more believable than this one on GB:

Underwood Elliot and Fisher M1icon Carbine stock : Rifle Stocks at GunBroker.com


Charlie-painter777