Hi Rick,
Glad the keys made it to you OK and will work.
Unfortunately, my underneath drive is on page 34 of the manual, yours is on page 31. Mine has a lever that sticks out of the RH side of the base. Tight is away from the operator, loose is toward the operator. My lever cams the motor base up so the belt can be moved.
You'd think your set up would be similar; use the weight of the motor to hold belt tension.
Looks like from the parts page you'd start by pulling down on counter shaft bracket 041-111 to get proper tension between the spindle and counter shaft pulley 560-025. Seems like cam O-244 would end up as you noted in question 1 for full tension on the drive belt. It looks to me from the parts drawing that the end of the lever O-281 is facing away from the cone pullies instead of toward them as in your pictures. If you flip it 180 degrees that should take care of the interference to the pin in the upper counter shaft bracket. It shouldn't matter which way you throw the lever as long as you have clearance to other stuff. Looks like the holes in arm O-244 and motor base 050-026 are right on top of each other so either direction would give you the same travel.
I'm guessing here, but I think the two collars (DL-259) are adjusted up to load up the two compression springs (O-276) to help lift the motor for belt changes. Otherwise you'd be lifting the full weight of the motor with the cam lever, the springs on the bottom give a little boost from the bottom end. I'd set it up by throwing the lever to tighten the belt, then adjust the collars up until the motor/motor bracket starts to lift. Might be easier to get the position by first lifting the motor with the cam lever, move the collars, then drop the motor and see what you get. Go too far and the cam lever will start getting hard to throw since you'd be over-compressing the springs. Just my best guess looking at your photos/parts drawings.
Best regards, Bruce