It works almost perfectly, with the only scenes ruining the tension being the crew riding along without horses. Otherwise, in a vacuum, you’d be completely convinced that The Holy Grail was a medieval drama, rather than the comedy treasure it is.
It’s true that a lot of humorous films, with the addition of the right music, transitions and titles, could be chopped and changed to be serious. But the Python lads were not only excellent actors, but dedicated to the bit and this takes the cut to another level.
Bad news is it’ll never be a real film. The good news? You now have an excuse to rewatch the actual movie, if you needed one.