these are the only markings on the heads. seems to be the date of manufacture and another code of sorts.
20170421 B2 55
20170422 A8 25
im assuming they refer to 04/21/2017 and 04/22/2017 but im not sure what the other two stand for

the heads come with 2 sizes of header bolt patterns. i dont think the ProComp or Speedmasters heads have the 2 different sizes. the Procomp heads also have a different chamber size but the Speedmasters are same chamber size. Speedmasters cylinder heads are however alot more costly and have alot more markings in them

Owner caption December 2017 · Photo 121 of 285