Arty,
Here is the problem...You either have the wrong frame for your body OR the wrong body for your frame!
(You have a later frame than you do for your body)
Please look at this article and refer to Fig. 18.
http://plucks329s.org/pdf/frame/Evol..._Assembly2.pdf
Either get the right frame for your project OR move the front body mount forward so BOTH carriage bolts, left and right, match the assembly of the carriage bolt holes in the bracket. I would think you need BOTH carriage bolts to mate to the bracket properly to get good body/frame alignment and stabilization.
Although during the transsion period, you might get something like this that you have as stated by Bob C above.