Don't know the exact details of trans guts on these but on others any interlock or detent that prevents going into two gears at once at the crossover gate can wear or break to do that. Outside synchro sleeve that moves to engage the brass can seize up on its' hub to do the same. Sometimes the little brake lugs (strut keys) that recenter the sleeve at neutral can break and pieces lock up the sleeve from moving. All those things could happen on the old B/W T-10s. I remember pulling the side covers to take a hammer/punch and hitting on sleeves to unlock them back out of gear when seized. Even had some less than fine quality shift sleeves crack in two at the fork groove to seize the works up, after that we scoured the land looking for the good rare solid body sleeves.

Always something simple but you find it when pulling down the trans. Maybe in the shift rail on these. MTX trans are very simple until you start adding in the preloads needed for front wheel drive types. Even those not hard but you have to pay close attention to the preloads or they get very noisy.

 I dont know the exact weight but I had mine out once tying to rebuild it myself until I found broken gears. I could pick it up and carry it around the room myself and I weighed all of 121 pounds back then.

Yep. These weigh nothing like a HD V8 4 speed. Though aluminum Muncies were pretty light......... ...the Mopar one was the killer. Best boat anchor ever.

We tried a couple aluminum cased T-10s, they popped the cases pretty quick. The load just sheared mountings ears off like popcorn. It was even a problem with iron cases. After a short time Pop (a professional welder by trade) had gotten pretty good at rewelding the cast iron ears back on.