A.)
You would wear the SLMC on your left side and order a left handed model.

1. IDPA Magazine Carrier Criteria
Magazine carrier must:
A. Be designed for concealed carry and suitable for all day
continuous wear.
B. Be worn on a standard belt of no more than 1 ¾” width that
must pass through the belt loops on the shooter’s pants.
C. Hold the magazine with enough tension to allow it to be
turned upside down and retain a fully loaded magazine.
D. Cover 2” of the magazine as measured from the top of the
cartridge rim down the back flat of the magazine tube.
E. Cover the entire front face of the portion of the magazine
inside the carrier. The front face is defined as the side of the
tube away from the shooter’s body.
F. Hold the magazine within 10 degrees of vertical (80-100° to
the ground) position on the belt, no substantial forward or rear
cant.
G. Be worn in a belt location that will position the front edge of
the carrier behind the centerline of the body.

And:

4. The shooter may
carry no more than two spare magazines on the belt.

It looks to me that the only limitation for IDPA would be that you could only have 2 magazines in it. I still think it would be advantageous that both your mags would be in the exact same place!

Joe

That, my friend, is the coolest thing since night baseball.

Congratulations!
Joe Allen