I recently bought and installed a Shimano Hyperglide HG 50. The cassette is all connected together except for the smallest cog. Came with a very thin spacer and a lockring. The old one didn't use the spacer, so I did not use it when I installed the new cassette.

The derailleur is SRAM, back before they got bought out I think. It was designed to work with the internal sram 3x7 hub but apparently also works with a regular cassette. Bike Friday said it is long enough to take up to a 34t cog.