The Mamiya NC 1000 is only available in black, and there is no silver version like there is of the Mamiya NC 1000 S. Another difference to the NC 1000 S is, that the focusing screens are not interchangeable. There is a special part (called curtain) in the NC 1000 which obstructs the change of the screens. This part is simply omitted in the NC 1000 S and, I assume, can also be removed from the NC 1000. This information is taken from an original parts catalog from Mamiya for the NC 1000 and NC 1000 S.
The specifications of the NC 1000 are almost identical to the ones for the NC 1000 S.
Joerg Krueger helped me to find this picture of a disassembled Mamiya NC1000 on the website of a camera repair service.