Four Speed automatic gearbox fluid & filter change.

[Odin 8]

I have replaced the automatic transmission filter and fluid on a 100 series four speed. There is what appears to be a method of filling the gearbox sump through the sump pan, like a periscope in the pan, to send the new oil up in to the sump, however, this wont allow for the full capacity of oil.
At the the side of the gearbox housing there are a couple of bolts (behind the front propshaft). Is one of these a filler/level plug?