In any case, any 300mm (non-telephoto) lens will have enough coverage that you won't run into the distortion (if it exists) before you run out of camera movements. Any of the modern (Schneider, Rodenstock, Nikon, Fuji) 300mm lenses will be just fine, but if you want a more traditional lens option without spending a fortune, a 12" Kodak Commercial Ektar would be a great choice. If your budget will allow more headroom, then a nice Goerz Dagor 12" would fit the bill. The G-Claron mentioned before is a great lens, but it will not be that cheap - they're known for their massive coverage and as such are sought after by th Ultra-Large Format crowd.