Also good to see they are making separate griddles to go on your existing weber gas grill. I bought a camp chef griddle several years ago and use that on my genesis more than I use the genesis as a traditional grill.
4 Burner dimensions -- The main grid is definitely correct at 34x19
Cooking Grid Dimensions 34 X 19 Inches
Main Grilling Area 646 Sq. Inches
Secondary Grilling Area 198 Sq. Inches
Total Grilling Area 844 Sq. Inches
For those who don't see full packers at their Costco, ask the butcher. Never have them on display at the Montclair, CA location, but asked and they had in the back. 16lb prime for $3.99/lb