I've got a Wingmaster from 1972, and I was having trouble with the online info. I called them and asked them. They'll be happy to tell you over the phone.
Barrel code determines yr of manufacture on Remingtons IIRC.
So with rigs of removable bbl..............has to have original.
Think the skeet models had bbl and receiver serialized (maybe other target versions way back?)
For checkering patterns etc.............visit Remington Society web site.