I have a 266BR on that same lift. I believe that the next size Econolift jumps to 8,000 or 8500 lbs. Gas weighs 8lbs/gal. A full tank would be 560lbs.
With gear, I'd say you should be right at the limit. I think you will be OK, but you might check with Econolift and see if there are any tolerances built in.