I found links to owners and shop manuals but they want $$ for them. You might find one or both useful. The shop manual was $70 or so which is a lot less than I paid for the Branson manual.
If your Montana was made by Branson then you're probably good with a premium fluid like Chevron THF1000 or Mobil Delvac fluid which TSC carries. Delvac is the new name for 424 which I have used in my Branson. It's probably a good idea to avoid the cheap J20A stuff.
My Branson manuals call for Chevron TDH and Mobil 1893, neither of which are made now. But I found data sheets and THF1000 and 424 both matched on viscosity.