You could build the camera to take 9"x9" lensboards unless you foresee problems with weight or bulk. A bigger board lets you use bigger Packard Shutters. My 11x14 B&J uses a 9"x9" board and so I can use a 8 1/2" x 8 1/2" square Packard with a 4 1/2" diameter hole. This permits the use of large Portrait lens like the 18" Verito. That lens will barely fit on a 6"x6" board, but then the shutter would need to be front-mounted on the lens rather than inside the camera.
Originally Posted by Nick Zentena
If the camera is built to take the 9" square boards, a lensboard reducer can always be made to take the more standard 6" square boards. I have such an arrangement and have also mounted a large lensmounting iris diaphragm to one of the 6" boards. With that setup I can mount all the barrel lenses I've accumulated and have a single Packard shutter for all of them. This saves cost and is consistent. The downside is the added weight and bulk which becomes important if backpacking. The tradeoff is flexibility vs. ease of transport. I'm more of a portrait/figure photographer so hauling a bulkier camera is not the greatest priority for me like it might be for a landscape or nature photographer.