Mckinney
I believe you are doing the best you can to get this old target rifle at least in a presentable state.
It certainly had a very close call to being burnt to a crisp & thanks to you it now has a home once more rather than be a rusted tomato stake in someone's back yard!
You've certainly done your research, again gone as far as you can go & like a lot of life's mysteries, that last door is still bloody locked!
When everything is done & said, it is your rifle, your pride & joy so let no-one take that from you. So take it out when you've finished all the hard work, load her up with some good match grade ammo & see what she'll really do.
I reckon she might surprise you!