I have a couple of Crosman 1377s. One dates back to the early 80s. The other one I bought recently when Wal-Mart closed them out for $25 each. I actually bought two of the newer ones but gave one to my 10 year old grand son.
I still have one of the old carbine stocks for the early one but haven’t seen it in years. The new ones are basically the same as the early ones except the old one has a cover over the breech while the new one has just a brass bolt with open breech area.
I did notice the new one said: “made in USA with some foreign parts. It seems just as good as the old one.
Your conversion of the .22 model is very common. I have never done one but it seems everyone on a forum I post on have done one.
The reason being is that the breech used has a bed tendency to not seat well over time, the barrel is too short of any real distance shooting & the air stripper acts like a brake & a bit of a suppressor, & able to mount some sort of optic on it, I still planning to keep some sort of peep sight on mine though.