I have one P-mag and one Slick mag on an XP-IO-320. Running an extra 2" of pitch over the recommended prop and very happy with the performance. It will still exceed 2600 rpm at 8,500 ft so once I go LOP it's all good.
I have 800 hrs on one Lightspeed and one Slick mag. Magnet on flywheel for the Lightspeed. O320-D2A with standard (70CM7S9-0-79) FP Senenich metal prop. Engine start with Lightspeed.
For your information I am putting together a small data base to help with getting this combination accepted in the UK. Having said that it has already been done here, I think its a case of left hand right hand!!