Last night I was able to rivet the two aft most bulkheads to the bottom tail cone skin. This wasn't an easy task, but I started with the inner most rivets on the aft most bulkhead, then started mounting the tail spring and working around it. Its difficult riveting under the spring because you are working at some acute angles in there with bucking bars while trying to keep those rivets straight, but it went OK.
I ran into troubles when I went to assemble everything, it seems the longer (lower) J channels interfered with the tail spring and caused the aft most bulkhead to skew in a weird way. I am really hoping it was the J channel because not sure what else it could have been. So I took it apart (again) and trimmed the J Channel, and put it back together. This time I put the tail cone on without the side skins, and will add them later. I think this is the best way to get a smooth fit, use an extra saw horse and don't put the side skins on until you get the J channels in the proper locations for all Bulkheads. You will understand what I am talking about when you get there.
Anyway, looking at the set up now, there doesn't seem to be any twist in the last bulkhead. It fits pretty nicely at this point and I hope adding the skin wont change this fit at all. So tonight we will find out.