I'm in the process of adapting an old 30x40cm (circa 12x16") camera to my own needs. The original holder is to be replaced with something more suitable for film, not plates, and lighter in weight. Are there any standards for the format? I'd rather try to make my camera back compatible with something that already exists in the world.

Slightly larger formats should also be OK. Say, a 13x16" or a 14x16"....

Thanks in advance.