The 433 is called the replacement head, aka twin plug head. This was the first aluminum head after the 65 heads. The ports had to be stock for use on 65 cars. Dual plug provisions for pro stock. This head was the everything head for Hemis for a long time, SS, top fuel, boats, pro stock, anybody that wanted to go fast. You buy them and send them to your favorite head porter, Mullins, Diamond, whatever. They are good heads and you can still send them out and have them ported and they will be anything you want. The problem is Edelbrock heads are the deal of the century. (They flow like ported 433 heads.) Edelbrock heads are the same price as ported 433 heads in 1975. Think about that. It's a good time to be a Hemi man.