E, Stock heads.. They made it as close to stock as possible. One head fits all. Just like their BB E head, it starts out closed chamber and small valve to fir those early 60s heads, 361-383-413-426 then a lot of work to make them like a 906. This means one is allowed to "machine" it to open up the chamber and big ex valve, porting in a sense, but still must maintain same CC, combustion chamber and ports. Now they allow any valve job and look the other way untill you stir up to much dust, but then you get a HP adjustment. High dollar game to play, better have a big wallet or the smarts before jumping in. My top piston ring will cost me $1400 (to play big league). So anyway, the stock heads are drying up so something had to take there place.
Now they let us run the LD 340 intake (Eldebrock, with factory part number) :-) even though none came on a stock engine from the factory, politics! Chevy-Ford guys are crying the blues!