After a little research, it appears you can upgrade your Ford C6 3-speed transmission with the quicker 1st and 2nd gears from a later model 4-speed Ford gearbox. It makes sense considering the C6 was the foundation for the E4OD and 4R100, and it's great to see this is backwards compatible!
This will really get my 1972 Lincoln Mark IV launching off the line harder. It also has roller/ball bearings (instead of thrust bearings) so it will likely put more power down and add to efficiency: both are always concerns with this monster of a gearbox.
I will probably pull the trigger on this conversion and report back!