I believe the head pipes are the same for both of the Borla header assemblies. If the rear exit setup is too loud for you, it will fairly easy to install the collector, mid pipe and muffler from the setup I have. To be honest though, if you have any doubts about using the rear exit headers, it will be too loud for you.
Paul, I asked about the modularity of the rear exit setup and basically, it isn't So, while the headers may be similar/same, chopping off the collector mufflers and tips and installing midpipes and a muffler would likely require a great deal of custom cutting and welding to the point it may just be easier to remove everything and get the LTH and muffler. Could be mistaken, but this was the impression I was given.
And do I have doubts? Heck yes I do. I've heard/driven a GT with the LTH and Heffner H-pipe. I realize the rear exits would be incrementally louder, but I think I can handle it. I've done as about an exhaustive search as one could do on threads here regarding this system, and it seems everyone that has done it has not had any regrets. I know Kendall took his off, but I'm not sure he necessarily 'disliked' them.
Only one way to find out, right?