The common R&P ratios were 5.44 (Scarce today) and 6.14
As has been stated.....The drop boxes could be had in 1.83 and 2.44
At this late date whatever is in the rear end is likely the result of what ever parts could be scrounged up when parts were needed.
The OC12 is a stout gear box and should be able to stand up to just about anything that the Spryte with the 6 cyl engine will toss at it.
The larger machines like the 2100 packmaster with the 57" tracks ...OR MORE and the V8 up front reefing on things really changed the course of how life went in the gear box.
Many times the loss of the rear ends WAS NOT due to the parts being too small/weak BUT INSTEAD to failure of thrust washers and a few other small parts that would shed pieces that found their way through the ring and pinion and also into the many bearings.
Once the bearings started breaking up the destruction increases mega times and the end comes soon after.
The compensator gears have steel thrust washers that are about 2" in diameter and the gears chew on these and shed metal particles.
The inner compensator gears have thin shim like thrust washers that also chew up and add to the mess circulating in the oil....
Deburring the compensator (Small outer) gears on each end helps stop a lot of the "chewing" on the washers.
There are two thrust washers ...one between each inner gear on the drums that are also a thin shim like piece..
These wear out and go away.
On my 2100 I machined1 the case and replaced the thin shim like washers with some very robust time proven thrust washers from automotive type transmissions .....
OC12 Thrust washer mods.
Drum to Carrier case thrust washer (Use Chevy TH400 rear thrust washer 4 tang type)..Machine case halves to accept 2 tangs.... Machine washer on back side so washer fits around radius on journal and lays flat against shoulder... (Make 2)
****Some tweaking**** of the tangs required to have the washer sit snug in its position on the carrier ****
Inner axle gear/s Thrust washer at center compensator housing (Use Ford A4LD Front drum to direct drum thrust washer).... Ford part number 84GT7D428AA (2 required) machine both sides of the inner case)
These mods will go a long way to curb the amount of crap being chewed up.
Another big issue is WATER
Water gets into the box.....causes rust in the bearings...Over time the bearing surfaces degrade and then "Shellout" occurs and the bearings really start to go away.....
The final phase of the bearing failure will see rollers/balls actually break up and large pieces get thrown into the oil pool.
These are HARD CHUNKS
Once they find the ring and pinion gears......GAME OVER....Teeth break and the box grenades.
The internal mods, bearings kept in good shape and the oil kept clean and free of water.
Anything in the way of metal coming out in the oil on a drain out should be taken seriously...very seriously.
There are normal wear items in these boxes.....BANDS AND THE DRUMS.....But this is very tiny amounts of metal.....FINE STUFF.
Always have a magnetic plug in the diffy and the drop boxes.
The gears in the drop boxes are huge and very tough.....They can chew up stuff readily but then it goes to work destroying the bearings.
Clean oil and inspections are key to keeping these bad boys doing their job.
The OC12 is heavy and pretty herky...but not that hard to get apart and repair.
The repair manual is available in data form here at the forum
The task looks daunting......NOT REALLY....just a job that requires keeping all parts in the order they came out.....
The machining of the inner parts to accept the thrust washers is a simple task that can be done by any machine shop with a mill and a lathe.
Simple math to calculate the differences between the original thrust washers and what is going back....= how much to machine off.
The steel backed bronze washers were designed with lube indents and a surface that can take some serious use...
KEEP IN MIND
The ring and pinion in the OC12 are large.....the parts used in the 1 ton 4x4 trucks that get the hell beat of them are not as big and they usually last pretty good.
The issues with the OC12 are due to FOREIGN MATERIAL (Junk chewed up in the box) and destruction from water that normally claim the parts and end the service life.....
****** NOTE*****
These nice little stones in a die grinder will work sweet to debur the gear teeth.
Notice the sharp edges on the small planet gear teeth....ROUND THE EDGES JUST ENOUGH TO STOP THE TEETH FROM CHEWING LIKE A CUTTING TOOL......Then the oil will generally keep the thrust washers in good shape
Good luck.