You are right, that one is rough. The brass sideplates are home made; you can see the "shadow" on the receiver where the original ones were. The receiver is .22 (the "dip" in the top front of the receiver proves that). The foreend and foreend cap should be the same as for the small tube (.25 and .32) rifles, so those parts would be no problem.
But in all honesty, the gun is so hacked up and so much of the surface destroyed that I doubt it can be restored in any way that won't destroy any value that is left. I don't think Turnbull would take on the job, but I could be wrong. You can call them and send pictures and see what they say.
There might be interest from someone who just wants a "relic" .22 to fill a hole in the collection until a better one comes along, but that would probably bring very little, maybe a couple of hundred dollars.