Originally, Rob Evan was slated to play the title roles, not David Hasslehoff. However, he left the show a week before the show was recorded and was replaced with Hasslehoff. A recording of a rehearsal with Evan was made and never released on DVD, but can be found online.
The trivia item below may give away important plot points.
At the end of "The Way Back", Jekyll falls over after singing the final note. This was not planned; David Hasslehoff had exerted himself so much up to that point that he passed out for a few seconds. Even as he gets up to exit, you can clearly see him staggering, as though he wasn't at his full energy and strength