W56 internals?

[tawneybuilt]

Does anyone know if the internals (shift forks, rails, ect.) of a W56 are different
between the W56-A/B (top shift t-case) and  a W56-C/D (forward shift t-case)?
My buddies 91 W56-C wont stay in first or third gear and I already changed the shifter seat.
Will any W-56 work for donor parts?   

[BigMike]

Internals are the same, just a couple of the shift rods are different.

Go ahead and swap out gears/bearings/syncros