Scott, you can't put the saginaw 3 speed overdrive tail on the muncie 420, sorry.
If you want to keep the granny low 4 speed. You can spend a bunch of money on a gear vendors OD for the tail ($2500+). You can put a ranger in front and then bend a custom shift rod ($1500). you can buy the advance adapters dodge NV4500 to chevy adapter kit and have an input bearing custom machined ($ depends on how cheap you can get the tranny).
I think I'm going with a ranger. If you decide that's the way you want to go let me know, I may have a pricing break.
Chris
