Personally, I would do a fair amount of research into the tranny your going to use the way your going to drive the car and mods your planning on making.

The old banna nose (61-63) birds were a pretty heavy car at well over 4000 pounds. That being said any engine mods your planning on making should concentrate on bottom end torque and let the HP numbers fall where they may.

The problem on a lot of intakes for the birds is hood clearance and this should be taken into consideration when choosing. One of my personal favorites is of course the Tri-Power set up. A word of caution, the 62/63 M series is a lower rise setup than the more common 406 style which will not allow the hood to close.

Althought other ratios were available the standard one for the birds was 3.00. Now combining the weight of the car with a lot of torque from the engine and sticky tires you going to put a lot of strain on the drive train when you put your foot in it from a standing start. Adding a high stall converter allowing will also multiply the shock the rest of the drivetrain will receive.

Considering the weight of the car an OD tranny with it's normally lower 1st gear ratio and a little deeper gear (say around 3.50s) should combine to give a fun car to drive. The OD feature should still allow you to have a decent topend and some type of gas milage. The 700R4may fit the bill pretty well, but depending on the year and history of the tranny you have, I would sure have a qualified tranny guy go through it to insure that it does have all the upgrades it's going to need to live in your car.