Turbo-350 trans. 7 J???

[Project_Gotham]

I'm visting my mentor, Mr. Harrison,(Tri-Five Guru) who has 2 1957 Hardtop Bel-Airs one soon to be in Chevy Rumble. And I bring up that the trans on my 68' Is leaking tranny fluid. So he say's
"Hey I got a fresh rebuilt TH-350 you can have for free"

It was supposed to go in his 56' racer that he sold about a year ago. So he gave me the tranny and a new 10' 4000-4500 stall converter.
Here is my question on the alum. bell houseing there is a 7 J. I have never seen anything like it. Can anyone help me figure out what it means?
Hope this is not a stupid question.