The complete exhaust kits are typically manufactured by either Motive Industries or Precision Exhaust. The intermediate pipes and mufflers are "ok" in terms of fit and finish. However, both company's H-Pipes are awful. They don't fit properly at all. I posted about this issue in the past.
http://www.concoursmustang.com/forum/index.php?topic=6815.msg39607#msg39607I had a terrible time finding a properly fitting H-Pipe for my "A" code. I finally bought a H-pipe from Scott Fuller Reproductions (Scott and I discovered that the "A" code H-Pipe and the "J" code H-Pipe found on '68 Shelby are virtually identical (with only a couple of minor differences). We both completely forgot that the "J" Code 302 in the '68 GT-350 uses the same "standard" log type exhaust manifolds that the "A" code 289 does. In fact, those two exhaust manifold are pretty much the same other than having different engineering and part numbers.
As a result, the only differences on the '68 GT-350 H-pipe vs. "A" code H-pipe are the placement of alignment tabs where the H-Pipe meets the intermediate pipes are in a slightly different spot on the pipe and the part number on the '68 GT-350 H-pipe is of course for a '68. However, once the H-Pipe is installed you can't even see the part number. Other than that, the dimensions, bends, flats, etc. of those 2 H-Pipes are completely identical.
I have 2 H-Pipes from Motive and they both fit terribly. One purchased in 2010 as part of an entire exhaust kit and one purchased separately in Jun 2013. I also sourced a 3rd H-Pipe from Precision Exhaust. The Precision Exhaust H-Pipe was identical to Motive part (the companies have a bit of history that ties them together and use the same designs). Based on some digging / discussions with various suppliers it appears that Motive supplies the majority of the reproduction H-Pipes for sale today.
The installation of the '68 GT-350 H-Pipe from Scott Fuller for my '65 "A" code was flawless. The only change I needed to make was to the "kit" intermediate pipes. They were too long for the proper H-Pipe and needed to be trimmed. Bottom-line don't waste your money on the Motive or Precision Exhaust H-Pipes. They just don't fit. The Scott Fuller H-Pipe is outstanding. It's premium priced but it fits like NOS.
Regards,
Ron