Well, I've gone off and done my own research, including contacting John Blichmann about the burners he uses for his Top Tier, since his system uses 55 gallon kettles. He felt that for my size pots (28" x 30" high) which are 67 gallons to the top and will hold 55 gallons of preboil volume, that I'd need 100-120k BTU.
Interestingly he cautioned my against over inflated numbers stated for burners like the KAB6, which I've seen rated at 210k but John estimates more like 68k. His burners are slightly different, though similar looking, use 10 PSI and create 72KBTU/hr.
I found this burner below and spoke extensively with one of the owners of the shop about this burner:
The page it's on is found here: http://www.tejassmokers.com/castironburners.htm
about 2/3 the way down.
For those of us planning on building this burner into a stand, some nice features and things to know:
* Use any length shaft between the gas line and the burner itself - it's just 1.25" pipe
* The top of the burner should be 4.5" to 5" below the bottom of the kettle. The gaps around the pot, created by the spokes that hold it up are critical as that is where the waste gases are discharged. The pot sits 3/4" above the rest of the stand to create that gap.
* Although you can use a 30 psi regulator, it won't suck down that much gas.
* The head alone is 6" in diameter and it weighs almost 11 pounds.
That's my huckleberry!