+1 on the back half and I'll go 1-step more....Throw it all out if you are going Concours. The H-pipe has been welded onto, so even
IF it is original (and I doubt it is), the correct system will no longer connect to it.
As an Owner of a muffler shop who is capable of building my own systems, although those Flowmaster Mufflers sure sound nice (sounds even better with larger pipes, like 2-1/4' or larger
), NONE of the back is correct, possibly even the trumpets are wrong unless perhaps the muffler shop welded only the tips back on. The originals would have different hangers and much more than that looks incorrect with the limited photos you shared. I'm looking for signs that this is even an original GT chassis.
Perhaps, seeing the hanger system behind the mufflers would help some.