I ran this setup 14 years ago on RU, purchased direct from Jegs at the time. The adapter plate sandwiches between the coil pack and ignition module. The harness just runs to the DIS-4 box. Hook up some ground wires, power wires and IIRC, you might have to tap into the tach lead but not sure. Set your dip switches for your setup and Wala. The loop plug, is if you want to take the DIS-4 out of the equation without having to dissasemble the coil pack and module sandwich to put it back to stock. It also came with two gaskets for the sandwich adapter as well some longer screws for the assembly, which I see in the ziplock bag. The boxes had a hit or miss record of good vs bad. Initially MSD warrantied and either repaired or replaced them free of charge. This was circa 2004 - 2007 IIRC. They eventually gave up and discontinued both part numbers, which IMHO, was a shame. I was lucky and mine worked perfectly. It definitely gave a hotter spark with extras like a built in two step. I think I paid around $500 for both part numbers plus shipping from Jegs back then. I bought mine in 2004 right after they made the adapter plate specific for 86-87 Turbo Buick and 89 TTA. The DIS-4 box, initially was created for MOD motor Mustangs. MSD saw the need for ignition upgrades for our cars and made the adapter plate. Even going so far as getting permission from Buick to use the Grand National emblem logo on the circuit board which was awesome! Now days, the TR6 has started dominating the ignition upgrade option. A lot of people got bad boxes and had bad experiences with MSD on their repairs and replacements. But some of us I guess, just got lucky. I definitely saw a difference on my setup back then. And this one for sale definitely looks NIB to me and is a good deal. I wish I had some extra cheedar on me, but with BG around the corner, no can do. But I would definitely roll the dice and grab those again. I wish you luck with your sale.
-Patrick-