Well I did it, the 78 King Cobra now has a 650 speed Demon sitting on top of it. I know the 650 is a little big for it but I am thinking down the road when we have this thing running High 12's. before I put it on I jetted it down 3 sizes primary and 4 sizes secondary. WOW does it make a huge differant over the old Holley that was on there. runs really good. Now I have to get new tires these are really bad.