don't want to discourage your enthusiasm... but i agree with the last few posts. it sounds like it's getting a bit complicated, contrary to what you're setting out to do! i'd just either trade or sell the arch for the one you need to match the pans, or vice versa. sell the drop flue pan and get a raised flue pan to match the arch... one that has float boxes. it's money spent now, but i assure you, you'll be much happier in the end!
Awfully thankful for an understanding wife!
“The only place success comes before work is in the dictionary.”
- Vincent “Vince” Lombardi
Good luck to all!