Kawasaki Z1R brake pads -- why different?

I noticed that the stock rear brake caliper on my 1978 Kz1000-D1 'Z1R' looks just like the standard model Kz1000-A2 bike's rear caliper, but the Z1R uses a different brake pad.


HERE ARE THE PART NUMBERS FOR THE REAR BRAKE PADS:
1978 Kz1000-D1, "Z1r" -- rear brake pad OEM part # 43050-1013

1978 Kz1000-A2, "Kz1000" -- rear brake pad OEM part # 43050-010


Now granted on these two bikes, the brake rotor is drilled (has holes in it) on the Z1r and the rotor is solid, not drilled, on the 'standard' model Kz1000-A2 bike.

Does that explain the different brake pads that Kawasaki used for the Z1r versus the Kz1000-A2 model?

What is the material or size etc. difference in the two bike's rear brake pads?

I would also like to know the answer to this one....................Bump

Z1R pads were sintered.