Kevin, cutting the end of the Agfa sounds a lot less fiddly than the mucking around I went through to get everything lined up properly. Putting the rubylith in the autographic window is a great idea. Sounds like you're almost ready to go out and take photos.
Jerry, I've got a Kodak 2C Jr. Autographic that is too nice to modify, but otherwise has great potential. The frame size is 73mm x 125mm (on 130 film) so not too far from 6 x 12 and spacers should work fine. Best of all, the entire back comes off so fitting the reels in looks to be very easy.