"It looks to me that it is the same as the one in Peters photos"

The photos were courtesy of amoretti.

His drive is a "regenerative" one, as this one is, but there are subtle differences from the one shown above.

My research shows that this drive, in various forms, was used in perhaps ten different Monarch tools, perhaps only one of these being the 10EE.

This drive is quite flexible, and can accommodate a spindle motor of just about any horsepower simply by substituting a different motor driver board.

It would be my preference keep this drive rather than attempt a sensorless vector or sensor vector conversion.

What was your reason for substituting an AP (cogged) belt set for the (cogless) A belt set?

Usually, I have only done this when the sheave diameter was relatively small, and extra "bite" was desirable.

"What was your reason for substituting an AP (cogged) belt set for the (cogless) A belt set?"

I believe that is the way it came from the factory. The 87" was a very low hour machine and it had cogged belts so that is what I replaced them with. I would think cogged belts roll easier and provide less vibration.

"Can you state the diameter of the holes, and the displacement from the slide bearing axes?"

The holes are 5/16" and they are 1.25 center to center. They were already in the casting when I purchased it. I would think that is was shipped that way from the factory.

My 83 has drain holes like that also.