First, this is *awesome*. I replay ultima underworld usually every couple of years because I love the games. Went to replay it this week, and stumbled on this, and its amazing. Thank you for doing this.
Second, found a bug that I thought was hilarious and thought I'd report it. In the Bullfrog puzzle on the 4th floor, there is a sign just floating in midair in the middle of the puzzle. lol
(and I know, you have no plans to do the second one, but man its going to be hard to play the second one normally after playing this one. lol)