As a Kit, probably not, but if you take your parts book to a full line auto parts store that has been around for a while, and has boooks, not just the computer, they just might be able to fix you up. You could alos go talk transmission shops that employee people with gray hair.
Look at Mac’s Auto Parts website. They show a complete gear set for ’49-’50 Mercury transmission. The set is $695. I was also able to find a complete gear set for a ’50 Ford truck (don’t know how much different) at C&G Early Ford parts. Price was the same.
I have a 3 speed with overdrive transmission from a 1954 Mercury. It is complete with wiring, cables and kick down switch for a complete conversion that I had intended to do to my 54 Mercury automatic. This might be the same transmission as the 50 Mercury and maybe not. You might want to check an interchange book. I do not have one, but I would like to sell the transmission. I believe it is likely in working condition.
John Polizzi firstname.lastname@example.org