This page lists the 40 pin rockwell "6503" as being a custom part # for the 65c02. Rockwell also made a "real" 28 pin 6503. The 338-6503 is probably an Apple part code signifing a newer 6502. CPU part code stamping is something that Apple likewise did on future custom ordered 65c02's made by VLSI. http://www.cpu-world.com/CPUs/650x/ - Paul