Problem solved!

Good news, the "Baked Belt" worked like a dream; I baked it at 120 °F for one hour and the belt practically slipped on (well, not really, I had to muscle it on a bit). I'm thinking it took me all of three minutes to thread it (once the tensioner was compressed) and thumb-press it over the last cam sprocket.

Success is so sweet; I'm now treating myself to a beer and a pizza.