I use them on my street cars. There were 3 main casting numbers used in A-bodies. The '65 model was unique. In '66-7 they used 2536563 for most applications, and a 2536771 for cars with C.A.P. (Cleaner Air Package). I don't know of any performance differences between the three. I won't get into the D-Dart or marine/industrial application discussion.....
The D/Darts came with the 2536771 intake that came on the w/CAP engines. Due to larger throttle bores, a 1/2" thick aluminum spacer was fabricated "in house" to adapt the Holley carb to the intake. The manifolds were not modified at all.
