I use the Sinar P as a platform for both 8x20 and 11x14. I've sent some photos to Jorge and I understand he is working it out for a 12x20. Using the P or P2 is a really beautiful system. I'd be happy to provide more details if requested. Also here is a web site that has some images of the 8x20:
http://www.mamutphoto.com/content/view/59/43/lang,fr/