I don't recognize the transmission, but it looks like there is a dipstick
plug on the port side next to the shift cable. There should be marks on the dipstick indicating the "full" level. The only question is whether the dipstick should be fully screwed in or just resting on the shoulder of the opening--I had to contact the manufacturer of mine to find out which (this info was not in the owner's manual.) Some gearboxes use 30 weight
engine oil, others use automatic transmission fluid--you should be able to tell which from the color, but it would be best to check the owners manual.
The stuffing box looks like a conventional Buck Algonquin. If the
boat is out of the
water, you can take out a segment of the stuffing and try to measure it.
I take it there's no nameplate on the
gearbox?
Perkins probably used only 1 or 2 gearboxes with that
motor.