Questions on 81-86 true widetrack duallies, with regular pickup bed?

[big rig duallie]

I have the shorter axle that chevy made, it measures about 44" from brake backing plate to plate. The question is: What is the backing plate to plate length on the wider track axle? Also what is the distance from the center of one leaf spring pad to the other? The target group for this would be from 81-87 trucks that were produced as true duallies with bed and flared rear fenders. All info would greatly be appreciated.

69'Chevy 1 Ton Narrow Track Duallie