CJ, thanks for the feedback. I expect a lot of people just skip the rack. I think I will want a big front bag on PBP, because I expect getting food to be somewhat problematic at some controls.
iTrod showed me the low rider rack from his coupled CoMotion. The struts pivot nicely on that, although I think it's just a standard rack. I was thinking about pivoting the tombstone, but I think having that fixed is probably okay. I would just make it as short as possible and still engage the bag. The decaleur makes up for a lot of slop.