[68bird400HO]

Originally Posted by starlightblack

a 1971 Trans Am engine date May 20, 1970?

Yup. These were the 455 blocks carried over from the end of the 1970 model run and used up in the 71 HO cars. There were actually three casting numbers for the 1971 455HOs. The first was 9799140 which was the 1970 carry over. Then 483677 was used on the early 71 455 blocks (castings from Aug 70 or maybe earlier). Then it switch again to 485428 which was your later 71 455 block casting used through 1974 (except SD).