Okay, I think what your trying to do is put a set of 406 heads on a 390 engine, am I right?? According to this these 406 heads shouldn't be used on the 390 because, too large a notch would have to be cut into the cylinder. A better choise would be the 428 Cobra jet heads. And they DEFINATLY won't go onto a 352 block. So, if your buying 406 heads to go on a 390 engine the book says not to do it.

Vegas