Call John 727-581-1700 - he makes custom jobs and rewinds factory heat exchangers, can usually offer better materials options.
We had him wind a coil for an old Century 400 Avenger 210 - and this dude gets HOT - I mean stupid hot - hot to a point that we actually have to have a second QD off the main solution output cracked open a hair to let off some of the heat.
And he did it using a much better grade copper, and for $450 less than the factory replacement would have cost.
http://www.hotheatexchangers.com/