Looks like they got rid of the slip fit on the back pipe and it is now welded? Looks like it fits really nice. I have a slant in my 64 D100 that i would love to upgrade the exhaust.
I got the one with the dual slip fit first. I think I may have been either the first sold fat-pipe or at least the first one that was going in an A-body. The one with the dual slip fit was too tall and ended up interfering with the steering cross bar. I took a bunch of pics and measurements and the guys @ Gill worked up a revised unit specific to the A-body and swapped mine out for the newer model. I don't know if they just completely switched to the new model or if they are selling both the a-body one as well as the original design for D100, but give them a call or email. Super nice guys and helpful- have even called me a few times to check in on project.