I did a little more research over the weekend:

The dizzy housings seem to be the same overall height:
I compared an LA TBI and an RB (so presumably LA, Maggie and B are the same also). Every other bare/unknown housing I have was also the same height.

The housings differ by:
1. if they have a slot for vacuum advance (all pre-LeanBurn carb'd cars),
2. no slot at all (LeanBurn cars and newer) or,
3. mounting ears for the screw-down dizzycap (Maggie).

The shafts differ by: the length down into the engine, and then the shaft up top (whether for points, VR sensor, TBI, or Mag). The points dizzys IMHO should be avoided, they look to be more difficult to convert (they have a 2-piece upper shaft - the cam lobe is a separate piece and it holds the rotor, and the trigger wheel needs to mount where the cam is).

Caps/rotors differ by:
The LeanBurn-older, the TBI, and the Maggie all use different rotors and/or cap combinations, so planning is required to mix-match the housings, shafts and upper parts.

End result:
It seems any engine, from A, LA, B or RB, could have a dizzy converted to the 5.0 TFI setup with the right combination of donor parts (Ford guts, Mopar housing of your choice, and shaft to match your engine).

Choose the shaft based on your engine size, then get the rotor that fits the top of the shaft, then the cap that mates with the rotor, then the dizzy housing that mates to the cap. Whether you seal off the vacuum slot or get a slot-less housing is a matter of preference.