I had one in my 65 Barracuda: 68 340, 2.02's, Hooker fenderwell headers (small port even) Strip Dominator intake, 750 Holley, 284-484 cam, MP 175K convertor (2200?) 3.91 rear. Light 'em up! Same cam and a STR-12 intake with a single Demon 650 felt a little slower but still spun em through 2nd. I liked it, 700 rpm idle in gear, about 750 out. Very tire limited back then due to fender lip. I heard the .509 cam was the dog!
My friend has the 509 in his 71 to do with the four speed in 391 it works pretty good in that damn good actually but he used to work in a machine shop he's done a lot of head work to those things and he's got like some kind of NASCAR intake on there