Winterpegger ;) - a 1975 164 uses 240 rear suspension, so an entire 240 axle will fit. It is the only 100 series car that that is true of.

The internal parts will all interchange. Just because they look different doesn't mean the bearing positions are different.

The SCCA ITB class has been dominated by 140's over the last few years. I have it confirmed in private emails that the vast majority of the successful cars run True-tracs. To me this type of moderate hp road racing is the closest motorsport to aggressive street driving, so on that basis I would have a recomendation to use the True trac over other brands.
Also, noted turbo 262 rallyist John Lane found the True-trac to be by far the most durable. He put through approx 500 ft-lbs of torque, eventually breaking the axles, but never the differential. He mentioned the Dana unit to be the weakest, and a ZF unit to be in between.
Dana axles are far more difficult to service than typical Ford 8 & 9", Chrylser 8&3/4 etc. Much more labour intensive and cannot be done out of the housing. A Canadian (BC)Volvo racer and rear axle service professional is Ian Wood. Do a search. He may rebuild a core axle that you could go and pick up.