the 87-88 b2600 was the same outwardly as the B2000/B2200, the main difference being the 2.6l 4 cyl from Mitsubishi. The frame is slightly different for the motor mounts and passenger side exhaust. Unfortunately they still use the same Nikki carb so the best upgrade for for performance is still a Weber 32/36 progressive, which will also get rid of that oily octopus on the drivers fender and the "canister vac" air cleaner. The 2.6 is both more powerful and more reliable than the 2.0/2.2 Mazda engine, and even more so than the later 89-93 B2600i which used a head cracking Mazda 2.6l engine.
Good find, they are still good trucks, as long as it runs well without smoke you will have a Mazda truck that will keep up with traffic. They didnt make many in the 2 years they were available, and the higher cost means they frequently had more options, like trailer mirrors and two tone paint..