Co planer is for band saw wheels, isn't it. A planer requires an offset between the two table halve, with the back exactly the height of whatever cutters you install. I have a 6 inch Powermatic and looking at it, I think the movable side is running on a carefully machined rail so it stays flat (parallel with the cutter). I'm wondering if one of the blades has loosened up and is lifting the board up slightly above the raised back end. That might explain the wedge shape you described. If your blades have lasted many years, are you sure you want to replace them with the Byrd head? The way the blades are cinched in is pretty solid, but the forces acting on them have got to be pretty powerful.
I think you are describing a wedge shape looking down the end so one side is thinner than the other. If it happened all at once, I'd bet one blade moved.
That powermatic is a tank, I don't think that other than bearings, there is much else than blades behind the mis-cuts.
The more I do, the less I accomplish.