In theory, since K7 PiezoDN curves don’t use shade 7 even though it is installed, there should be no difference between a K7 and a K6 PiezoDN curve, BUT the quads are not the same since P2 has the PK ink in the Y position rather than the K position.
You could remap your existing linearized K7 quad to a K6-P2 configuration. If you have the PPEv2 toolset this is fairly easy. Or you could just start over with a quad from the folder in my earlier post. Since you have been away from this for a while it might be better to recalibrate from scratch, but the choice is yours. You should at least verify (and relinearize if necessary) if you choose the remapping option.
About paper for proofing, I don’t remember what I said in the past, but I use a double-sided paper like Moab Entrada, Canson Rag Photo Duo, or similar, since I can use both sides and they are a decent approximation of the surface texture and base-color of the standard alt-process papers like HPR, Platine, etc.