I had to give up on the rails for now. I need to perform a deep clean of the Hotend, and also the feeder pulleys. Sigh...

Anyway, I just finished downloading the latest Jessie Lite from Raspberrypi.org and loaded it via Win32DiskImager to one of the SD cards. Booted fine on the Raspi Model B.

I'm going to use the Raspi B to build the packages up that I want, as it has the same basic architecture as the Zero.