As Ralph says you won't need bag bellows. However you need to check because I think the MPP actually uses a cone not a recessed board for a 90mm lens, this is so the standard sits in the body while the front is dropped so the opposite of what you'd expect. This would make sense as with a Pakemaker Graphic at Infinity a 90mm sits just on the outside of the caseing on the drop-board.

A 90mm lens needs significantly less movement than a 150mm, it's more responsive to slight rise/fall/shift/tilt etc and so even with a cone you should have enough movements.

Ian