Claybe:
While I wouldn't bet my ranch on it, the photos of your damper and heat transfer pipes led me to believe you may have a Superior HeatForm manufactured fireplace. Does the fire box have ribs that protrude about 3/8 of an inch? If so, all the more evidence that it's a HeatForm. In any case, even if it is not a HeatForm, I think that you will have to cut away two of the heat transfer pipes.
We installed an insulated 6 inch SS liner down a 14 inch by 14 inch terra cotta flue. But in order to get the liner down and connected to the insert, we had to cut out the damper and then cut away two of the four heat exchange pipes on our own HeatForm fireplace. We also had to cut away some of the HeatForm steel right around the area of the heat pipes.
As I was thinking about how hard it might be to cut away that steel - the HeatForm is constructed of 1/4 inch boiler plate steel - I decided against using either a reciprocating saw or a right angle grinder. So I brought in a welder who used a plasma torch to cut out the damper, two heat tubes and the steel necessary so that the SS liner would clear. As it turned out, I had to bring him back a second time to take out additional steel as "flexible" liners are not as flexible as we might want them to be.
It was Dirty Harry (Clint Eastwood) who said "A man needs to know his limitations." It's true. I was not confident that I could cut this steel with my tools - and I did not want to use a plasma torch as a do-it-yourself project. So I brought in a pro. He did a great job and he also welded my block-off plate in place as well. I have never regretted using a professional welder to help me with the hardest part of the Hearthstone Clydesdale installation.
See also for details about the construction of the HeatForm:
http://ia600702.us.archive.org/29/items/HeatrormFireplaces/HeatformFireplaces.pdf
Good luck with your installation project.