Hi T-Willie....I can add a little more info to this as I am in the process of putting a transmission in my Scout project. (152, T18, D20)
What I have found so far is that the T90 3 speed has a different mounting pattern than a T18 or T19. So...you might need the correct bell housing with proper clutch disengagement method (hydraulic or mechanical). You may also run into an issue with driveshaft lengths when you start swapping components around. Nothing that can't be overcome....just something to be aware of.