RL02 version of UNIX6?

Yes, that's another copy of the Shoppa disk. So, I looked at that system, to see how it dealt with the clock issue on an 11/23 (in /sys/ken/main.c, if anyone else is interested). While looking, I noticed something that made it extremely unlikely that it would boot on an 11/40. Sure enough, attempting to boot the /unix on it on a (simulated) -11/40 blows out. There are a couple of other unix loads on that pack image (oldunix, unix.tmp, etc), but all the ones I looked at had the same issue (only tried booting the 'unix' one, though); they're probably all for the same machine, so have the same configuration issue. V6 Unix was pretty persnickety about the hardware configuration it ran on; while it was possible to create builds that would run on almost any configuration, on 'vanilla' V6 that really only applies to the /40/45/70 era. And even then you still had to re-build the system to match your actual hardware configuration, almost all the time. The advent of the /23 (with no CSW, and no KW11-L/P), made things more complicated. (The clock is pretty key - Unix needs one - several things, e.g. parts of the teletype drivers, require real-time delays provided by the clock. I've never tried to run Unix without a working clock, I'm not sure if it would run without slowly grinding to a halt as stuff waited for clocks delays that never happened.( With a little work, a suite of 'universal boot' versions (one for each type of disk controller - RK05/RL02/RX02 etc) could have been created that would boot and run on any pretty much CPU/etc configuration - at least, well enough to build one that did exactly match the hardware configuration at hand. (The one on the Shoppa disk is close, from what I could see.) I don't think anyone ever bothered, though (in part because it was much more of a PITA to test them all, BITD, with only real hardware). Noel