The 501C body is basically a 500CM with some cosmetic changes to make them less expensive to make:
- different shutter release button
- Acute Matte D screen
- no 'body ready' indicator
- non-detachable crank
- no GMS
The 80mm CB (marked 80C) is optically a different lens, that was slightly less expensive to make. In practice, the images are indecipherable from the C-CF-CFi versions, but the theoretical MTF curves are slightly better for the latter, hence the preference for them.
The Acute Matte D is a plus, if it is still installed. It was a very nice kit to use, and was a way to introduce people to Hasselblad with a new, instead of a used, product.