
That must have been a universal pump for a lot of GT hydraulic systems. My W.H. has the same unit and I know C.C. used it too.
My wheel horse manual has a parts breakdown for the pump if you ever need it.
Here's what it says about the pump oil level: ''Remove filler plug and fill to top of hole with fluid. NOTE: Filler plug is mounted off vertical center line of unit. This is to prevent over filling. An air space must be left in the top of the tank, so no attempt should be made to completely fill reservoir."
It looks like the filler hole. in your pump, is in about the same position as the one on my W.H. so I guess the instructions would apply to your unit too.
I almost forgot. It says to "Replace plug and tighten"... just in case you didn't know.

Bill