['ol Pinion head]

Early production '71 HO heads indeed had no external date codes, the center head bolt hole machining process removed the casting core date code. Sharing the same fate were production installed '722's & 614's.

"Late" 71 HO heads began to be cast Dec 4 (L040). The 4th was a Friday, & in over 3 decades, I've only ran across a few cast on that date. The following week, a good sized run of L080's were cast, then again on Jan 8th.

Have often examined an original mid to late production '71 455 HO factory assembled engine with an L080 & an A081 dated head. So many times, its more of the norm. Those two dated heads, paired together, is very common on factory assembled HO engines assembled through the late Winter & up through the Spring of '71.

With a few assembly plants still shut down from the Fall UAW Strike up into mid to late Jan of 71, & with HO engine stock on hand at them, those plants used up what assembled HO engines were on hand & the result is what some don't understand, the factory install of 9799140 casting early '71 HO engines in into Feb assembled HO cars coming out of very low production plants like Framingham & Oshawa, as well as higher volume HO install plants like Norwood.