Sounds to me like the tranny is bad... as far as the tranny's you got out of other Montes there shouldnt be any difference unless one would be a TH400 or different tail shafts for some reason.. Torque converter would I think be up to you... I would replace it if you have another with the other tranny's though... These guys will prolly be able to help you out better but I tried
Good luck, Tom