The same crap... 8) I have "516" casting heads, which were used on alot of 413 passenger cars. Mine have the 1.74" exhaust added, a light mill job, and a bunch of porting. For the money to have another set made, Edelbrocks would probably be cheaper. The closed chamber on these do get me to 10:1 with flat tops, which I understand is difficult to do with many heads in a 383.