Thanks for your reply Nyerguds. I've tried that resolution, it gives me an even larger black bar on the right side of the screen. I must have tried every custom resolution permutation possible, I'm getting either a black bar on the right or one at the bottom of the screen. I've actually found 1024x768 using the original aspect ratio to be a good compromise (two small black bars either side of the screen).
My apologies for not reading the Readme file first, it explained a great deal.