Speedo won't be an issue. Unscrew the electronic part from the 91 T-case, and your cable will screw right on.
Is this for a 4wd swap? If so, you may need a longer speedo cable.
Yes, it matters what motor the AW-4 came from. Due to the extremely low amount of 2.5/AW-4 combos made, I'm guessing it's from a 4.0. If it's from a 2.5, the bellhousing and converter will be different, as will the TCU, and I believe the trans itself will be set up differently.
What happened to the 96 T-case?