The only "MAIN" difference between a "single rear wheel" Eaton HO 7,200 and the HO 5,200 is the size of brake drums on the 67-70. That changed in 71-72. These years, the lug studs vary from 1/2"(3/4ton) to 9/16"(1 ton) and brake cylinders(because now 71-72 have front disk brakes, which required a different size brake wheel cylinder for rear)......the HO 7,200 had the 9/16" and larger drums while the HO 5,200 had the 1/2" and smaller drums. The except to this is the HO 5,200 in the K20's......these had smaller drums (BUT with "cooling fins" cast in them) BUT had LARGE 9/16" lug studs. 67-72 Eatons all had the ring gear deflector. The differental housings and 3rd member drop outs where all the same....(except of course the gear ratios and "D-lockers" options). There is also slight differences in the types of brake lines used and placement throught out these years....so not all 67-72 Eaton brake lines are interchangeable. One more thing....The 67-70 HO 7,200's brake backing plates are also NOT interchangeable with 71-72 HO 7,200's. They will bolt on but your brakes will not work properly without changing either the brake proportioning valve or changing the FRONT wheel brakes to match...this is also true for the HO 5,200. I am NOT an Eaton expert by any means...........These are the differences I have encountered through my years of experiance with the 67-72 trucks ONLY. I hope this helps you out.
Take care!
Jim "69oldie"
