Graves designed their 3/4 system in such a way that only their end can will work, no other can, stock or aftermarket, will fit. It's quite proprietary.
As an aside, yesterday's dyno runs proved something interesting. The MJS mid pipe combined with the stock end can gave us, after altering the fueling to suit, a low-end just a smidge better than stock, a healthy bump in the midrange, and a top end that actually was lower than expected. KC put it down to the cobbled together system that is really not optimized for best flow. I replied that for now it'll do, but after serious suspension work next month, the next (and hopefully final!) step is a full system. On the fence between Arrow or Graves.