I don't have any printed information on this old cat, but I am old enough, and enough of a cat tech to have worked on these when they and I were young, and still [kind of] remember these units.
if the bell housing is filling up with fluid, the most likely cause is the pickup screen in the fitting the hose on bottom of the trans. (provided this really is a standard wet-clutch transmission, [there were a few transmission options, including a true hydrostatic transmission]). this screen is to the inside of the trans and will not be seen unless you take the fitting out of the trans case, that the hose is connected to. this is a very fine mesh screen, and will be where the flow (out of the bell housing) is most likely restricted.
The parts diagrams/numbers are still accessible but your going to find someone who has some old service manuals for anything else.
I doubt any cat dealer would have any info on this older unit. Cat got into bed w/Mitsubishi years ago & all the older cat's took the hit when it came to parts/info, etc.
I am the mechanic who disassembled the old cat. There was quite a bit of fluid in the housing. This machine in particular doesn't have a nozel, just a fitting on top of the bell-housing. By chance does anybody know of an old Cat dealer that may have some info on this old truck?
The cat's I've worked on pull from the tank & spray into the bell housing. It does sound like yours is plumbed backwards. If memory serves me right there should be a nozzle assy on the upper part of the bell housing to spray the oil onto the clutch disc.
You could eliminate the wet clutch set-up & just install a normal dry clutch set-up- I've done that on occasion.
Usually when there's too much oil in the bell housing the starter begins to leak because of excessive pressure. How much oil was in the bell housing when you removed the clutch assy?