There are multiple posts on the topic. Most of the clearance issues are related to the rear transmission cross member . Most of the posts are on the 1/2t and it appears that rear trans cross member is often missing and maybe was never present.
Some of the brake upgrade kits mention a aftermarket transmission cross member is required.
The 3/4t with the drive shaft support bearing the cross member is needed and some report modification to the cross member for booster clearance.
Transmission cross member post
https://www.stovebolt.com/ubbthread...9/6/rear-transmission-support-sm420.html
