If you want it to continue to be a 3/4 ton truck why put a halftone Ford diff in it
Dana 60 or h052 are stock in these trucks
73 to 87 14 bolt fit well for width
There are disc brake options for all three diffs
Captain fab on the board here makes a few diy brackets to convert to disc brakes
Here is thread on the subject
http://67-72chevytrucks.com/vboard/s...d.php?t=786391
http://67-72chevytrucks.com/vboard/s...d.php?t=183452