1964 Barracuda 904 swap

the physical part of putting the trans in is no big deal. it's all the peripheral stuff that's "gotchas"

you'll need a kickdown assembly for the trans (aftermarket cable is easy)
fluid lines for a cooler-- external if your radiator is not so equipped
shifter, aftermarket floor is easiest
driveshaft will need to be modified. 904 is shorter than a833, the output is dependent on what you have currently and what you're going to. basically flange mount or slip yoke.
This is what I have B&M shifter after market cooler I can make the lines I know the driveshaft will need work is Flange mount kick down I'll use the Locar like we used in my kids truck I guess my biggest concern is the mount for the transmission is that going to need modifications it has dual exhaust that is out of the way and I guess my next question is what headers are people running in that car