The photos really help. What I see in a Springfield Armory rifle, made in June 1944. It has been completely rebuilt, probably multiple times, & I haven't seen any parts, other than the receiver, that are original. So, no need to worry about "matching" parts, like most rebuilds it's all mixed. The SA barrel was made in 1967; I don't know that you can use anything except a USGI M2 ball round as a "poor man's muzzle wear gauge". Commercial bullets aren't necessarily the same shape. (If the bullet is swallowed by the muzzle with M2 ball, the barrel is likely shot out.) The stock appears to be USGI birch, which some civilian attempted to stain red; I can't tell how bad the crack is.

Your real problem is the rust; this is what typically happens after a couple of years of storage in a wet basement or rental locker. It's pretty bad, affecting critical surfaces on the receiver, trigger group, even the chamber. Rust is not a "coating"; it is a LOSS OF STEEL. Rust (ferric oxide) can sometimes be safely removed, but the surface would need refinishing. I think that it is too extensive to be removed with Kroil & a bronze brush. In its current condition, I don't think your rifle is safe to shoot.

If it were my rifle, I'd send it to an armorer (a gunsmith familiar with military firearms) for a "technical evaluation". As long as the receiver is sound, every other part can be replaced. Chuck Moline at Warpath Vintage, posts on this forum, & will be glad to talk to you.
Phone 720-841-1399
Email: molinenorski@msn.com

This is just my opinion, others may vary. But, this is a high power rifle that you will fire a few inches from your face; I just don't want to see you hurt, I'd rather err on the side of caution.

Neal