Gus - see if you can find a copy of Book of Buckskinning 6 (it's out of print, but usually available through library loan). Well known period leather crafter Steve Lalioff has an article in there on making bags and IIRC discusses finishes.
Also check out Eric Myall's (used to work at Williamsburg) series of videos on making 18th Century leather goods -
http://backintimeleatherworks.com/images/SalesFlierpdf.pdfThe website is no longer, but here are phone numbers that are supposed to be 757-564-9659 757-532-1970
One finish that I've read of at least for the early 19th Century is dubbin - usually a mix of beef or sheep tallow, oil, and bees wax in varying amounts.
I remember folks talking about linseed oil and neatsfoot oil. Were these made differently than what is commonly available today?
In general yes........
Best quality linseed oil was cold pressed and then heat polymerized dependent on final usage - Tried and True Oil
sells a good version of the latter as do most better artist supply houses. Pure unpolymerized linseed oil can be bought at artist supplies or at health food stores where it is sold as flax seed oil. Linseed oil was a main ingredient in making the finish on patent leather.
Neats foot oil was once only secured from cow hooves and lower leg bones. Since the 1930's according to the folks at Lexol, any oil from an animal source that meets a certain Mil-spec can be called neats foot oil - most today is produced from lard.