I've also flown Monarch's A300, MAN
. I managed 4hrs on it, its no different to other aircraft charters used as far as seat pitch goes - just hope you don't get put in the middle row. The seating is 3-3-3, apart from the last eight rows and the very first row which are 2-3-2. Monarchs A300 seat 361 - the same as their DC-10 carried. In my experience with them, they seem like the best charter airline in the UK, always a happy crew, good service for a charter and a nice mix of aircraft to fly on.
And yes, all the info about MON
's A300 is on their website...
Hope that helps