I have a nice rebuilt 400 for my 78 Bronco, but I'm wondering about the rest of the drivetrain.

Mine is currently a C6/full-time NP-203 setup. I would like to convert it to an NP-205 at least, but I could do a part time conversion to the 203. What about an AOD swap? You need to mill off the cast-in bellhousing and purchase an adapter for the "big block" bellhousing. I like the idea of a tall overdrive since I will be running pretty steep gears eventually. What would it take to mate an AOD to an NP-205, NP-203, or even a Dana 20 with its better 2.5:1 gear reduction?

 

Most dana 20's came w/ 2.03-1 gearing. And while it is a good cast iron tc it was meant to be used in much lighter vehicles like jeeps, early broncos and i/h scouts. Dont know that it would hold up to the weight and large tires on a heavier bronco/truck. After further reading I see that alot of dana 20's came with 2.46 and 2.34 ratios.

 

I would look for a 460-bolt pattern E4OD. Since it was originally attached to the big blocks it will obv have the 'nads to handle it. AODs were only put on small blocks for a reason, unless you are willing to dump $ into it to strengthen it, be ready to replace it fairly often. While you will need a shift controller for the E4OD, it will handle infinite light offroading in stock form since it's modeled after the C6