Better late than never.. I ended up using a shop called Hudlow Axle in Rossville, GA to swap my original axle for a 1977 F-250 (Dana 60 with the ratio changed to 3.55).
My original 8 lug rims fit just fine and still the original 3 speed transmission. Only the e-brake was a little challenging to configure.
I'm very please with the results - the truck easily cruises at 60 mph with 2800 rpms.
Thanks all for your great advice!
Dave
