I've been doing 10 gal. batches for some time now and have decided to start using a gravity-fed set up. I've done a lot of reading on burners on a lot of the HB boards and decided to get the Bayou Classic SQ-14
for my boil keggle and use my current (cheap round burner) to heat my HLT water kettle.
From what I understand, the orifice size is the determining factor in using NG. The orifices (essentially the gas jet) vary in size depending on the fuel source and pressure. Natural gas is supplied at very low pressure and uses the largest orifice. Propane uses high pressure and a small diameter orifice.
IMO the ring type burner casting shown like the one shown in the SQ-14 is the perfect choice for home brewers. It combines horse power with efficiency, burns very clean and had good heat distribution. The SQ-14 can't be beat for price and all around great performance. For use with a DIY set-up, I think I'd buy the separate casting and an adjustable high pressure regulator with the appropriate orifice.
I have read or heard from many homebrewers who say that the jet burners (looks like a pipe with an orifice jet inside) and the multi-jet wok burners are lousy for our purposes, with the wok burners being the worst. They have no provision to adjust the air/fuel ratio and they use a lot
of fuel. They are designed to be operated at near-wide open throttle and burn way too hot. They are also expensive and look cool, but that's about it.
I'm sure others with some hands-on propane-to-NG conversion experience will chime in here but that's my 2cents.