Thanks again Dave.
I ordered a reverse ring with 52mm thread and micro-four-thirds adaptor - this lets me fix any lens with a 52mm thread to my Panasonic GH1, and as long as I have the "shoot w/o lens" menu option set, I should be able to use manual mode to set the exposure.
The problem I seem to have stumbled across, is that the Canon 50mm FD f/1.8 lens which I thought could be manually set, needs some kind of connection to a body in order to allow stopping down of the aperture to the chosen setting..... i.e. if I pick f/4 on the ring, the iris won't close to this setting unless I press something.
I have no experience of old manual lenses (you can probably tell), and I missed this 'stopping down' piece of the puzzle - I may be able to fashion a 'hood' which pushes the connections down and allows manual aperture setting on the lens to stop down the iris appropriately. I just don't know now!