A little help needed.......

[mopars0]

A buddy is cleaning out his garage , he has (3) 69 , 440's blocks
(2) casting # 2536430-10
(1) casting # 2536430-5



I know the 2536430-10? were ( 66/72 ) 440's ..Does anyone know what the heck the last numbers means... the one that I have in red. I've seen them in all ranges.

Thanks Guys......