I no longer have this car, so I can't help with dimensions - maybe Tom can help there. Aside from other body condition issues with that car, I discovered that an automatic tunnel is enough wider that with my large feet, I frankly didn't like what it did to my right foot/gas pedal accommodation.

The other factor was that once an overdrive is installed, the suspension of the rear of the engine, trans and OD seemed kinda funky. The automatic bolt locations being rearward of the standard mean that angle iron extends forward to pick up the weight which with an OD then extends rearward. Kind of a strange cantilever with the addition of even more weight. If I were doing it again (with an OD) I'd probably want to relocate mounting points forward and modify the trans support crossmember so that it picked up the weight and was mounted to the body, right under the transmission.