Depending on the make, many older guns have forums unto themselves with folks who most likely can help. otherwise, doublegunshop.com is also an excellent resource for older double guns
There is a book,"Best Guns",by McIntire,I believe,according to my fuzzy old memory.Its all about fine old American doubles like yours.You owe it to yourself and your shotguns!!
It will tell you what you want to know.
