I believe that SC meant "Standard Cell". That would make the 87157 just another part number, between the 87156 and 87158. The "P" probably meant a 40 pin DIP package.

Toward the end of the color computer, Tandy made a number of ASICs with Motorola (now Freescale) to cut costs. I suspect that is what you are looking at.

At the time, Motorola was fighting Intel with the 68000 versus the 8086, and with the 68HC11 vs the 80C51. It is unlikely that they would cooperate with an 87C152 second source.