Yeah, the 3 speeds didn't have a reputation for being "cool" even back in the day.
They were kinda a "granny" transmission, you only had to make one shift while driving around town.
I'm pretty sure that everything just bolts up. I've never done this swap though, and there must be a few tips to simplify things.
In the future, you may want to post your threads in the Classic Mustang forum. Many of the guys that own classics, just hang around in that forum, so they may not ever see your post.
The guys in that forum are very helpful and will likely be able to answer any questions that you have.