Anyone know of any structural & gross weight differences between the 0-0-2s and any of the 337 models? Other thing is is there an STC for hanging 550s on either airframe. I know there's a website that gives all the STC info, but I lost my bookmarks with the last HD failure. Seems that the 337 is the prefered airframe for fire spotting and FAC contracts here in Aus, and I'm thinking to add a 250-300 gallon hopper for retardant or fit a spreader underneath it for top dressing pastures. If that part doesn't play out, I'd prefer a set of IO-470s for the FAC/Spotting work.