I did a little searching on the 'net' and it looks like quite more of a challenge to set up a Dana 80.
I really don't mind the 5.13 since I'm going with a tire that's almost 46" tall (445/50 R22.5) Super Single.
In my application I don't expect to be running over 60mph, and i can wait for another gear and carrier.

Are You using your "stock" steering box? Is it non-power or power?

I got a power box from a GMC school bus to run my Hydro-boost, but MAN.. That hole for the pitman arm looks B I G compared to my little hd3500 center-link tie rod end.

Is it possible to post pics? I'm going to try and compare to see if just MAYBE the spindles can swap on the orig axle beam.
I'd like to see what you've got since I've got a '64 C50.

Errol