I think the HO72 will have a ring gear deflection pad adjustment beside the pinion, looks like a bolt or screw is all.
The smaller axles shouldn't have that.

The HO72 should also have 8 lug hubs, and yours are 6.

The sure way to get the bearings and seals you need is remove the old ones and check the numbers and or dimensions.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-