I may have located a 14 bolt with a 4.10 ratio that would be a viable option for the swap, they are confirming the width. The reported mileage is low but I suspect that the odomter has rolled over putting it at roughly 137k miles in a 1986 stake bed truck running a 350 with a 4 speed manual transmission. I am guess a farm truck.
I have not been able to determine prices for all of the conversion parts required but it appears I could likely obtain and modify the 14 bolt for less than the cost of the disk brake conversion for the Eaton. The 14 bolt would provide a better final drive ratio (4.10 vs. 4.56) as well as better parts availability so even at a wash in cost it may be a better choice but I would appreciate feedback from others.