Langdon's is a converten stock type GM unit, if I'm not mistaken. I'm not sure about the Jim Carter unit. The one from Patricks is actually an aftermarket Mallory Unilite based dizzy. I have an older version that's the magnetic breakerless. Neither version has a vacuum advance. I like how it performs, but it did need to have a spark box added to get it to work with the suggested coil. I've heard that langdon's is the easiest ot work with, so that might be the best one to go with.
