It really isn't amazing, Mudlark--the truth is that in the 40 odd years I have been hammering away at the guitar, I've stumbled through progressions like that so many times that they've finally sunk in--

Technology deserves some credit here--I found an MP3 of the tune, using Limewire,(I have it, somewhere, on vinyl, but my turntable needs to be fixed, and I don't have any idea which of the twenty five boxes records it is in anyway) which is better than vinyl because you can stop and replay between any two points simply and quickly and, for some reason, it is easier to play along with a music file played on the computer than to anything played thru the stereo anyway--so it was easy to refresh my mind on how this old piece went--

Anyway, I am really pleased that my explanation was enough to get you up and running on this--