they won't ? that's odd , I installed a 69 C barge HP manifold on my 69 with factory K , not a DC K , and a 383 and though I didn't try to make a headpipe , it looked like it would clear with a dimple in the headpipe ? But I can see the angle mill helping that out , considering every 35 yr old plus HP manifold I have bought has needed to be planed because they are warped , it's probaly a good idea to get that one angled ...