I know this will probably be of limited interest to the forum on the whole, but since my ACB-310 didn't come with instructions, I thought I'd put up some reference photos. Here's the new rear out of the box next to the standard kit.
Actus_ACB310_1 by Bradley Clemens, on Flickr
First step is to remove the bellows. Then adjust the geared focusing so the rear standard is as far back on the camera as it will go. This will give you room to work. Then slide rear standard back on the rail until the stopping screw is visible in the hole, like so...
Actus_ACB310_2 by Bradley Clemens, on Flickr
Completely remove the screw using a 1.5mm torque wrench.
Actus_ACB310_3 by Bradley Clemens, on Flickr
Slide the existing rear standard off, slide the ACB-310 on, replace the stopping screw, and... voila! Wide angle nirvana (or as close as you're going to get to it without popping for the Actus DB and a digital back).
Actus_ACB310_4 by Bradley Clemens, on Flickr
It'll be a pain to haul around the extra rear standard and bellows to switch between the two, but I will probably do it since changing them is so field-friendly. Also, the amount of extension possible should allow for the use of, at least, 645 lenses with the appropriate lens plate, so there's that option as well. I can't wait to get out this weekend with the APO-Grandagon 45 and see what it can do.