Spindle taper is # 4-1/2 Morse
I've had my lathe 14 years with the original belts and would use some
sort of link belt for replacement rather than dissasemble the spindle
and countershaft.
For power crossfeed you move the feed lever to the right and down.
Longitudinal feed is left and up.
I think the knob you are referring to engages the backgear. If you
engage it the spindle will lock up until you pull out the pin in the
gear on the spindle. You will now be in backgear.

I have a 24 page parts and instruction manual, much of which is
irrelevant information but if you want any specific info I could scan a
page or two.
Engineman1