I don't know if this will help. Here's a gearset that will give you .80 overdrive. Modern Driveline Looks like you would have to upgrade to a Ford Mainshaft though.

Here's some ID numbers for T-5's. Looks like some of the F Body cars had what you were looking for. British V8


1954 3600 Chevy Truck
"The Fake Truck"
In the Stovebolt Gallery
More pix on Photobucket