While you are putting brakes on I would "strongly" suggest you replace the front brake lines also. On the Ford 1999 E450 super duty you have to buy OEM only but well worth the price. A known failure for this chassis as it ages.
The 'brake lines will look perfectly fine' BUT they fail on the inside. The inside collapses.
Been there did that. Replaced the brakes only, on the same make and model you have and coming off an interstate ramp and the brakes went out. :E Thought for sure I was going to die.
Truck stop repair knew right away it was the brake lines. Just saying since you've got it apart I would replace the brake lines also.