9-6-60 383 casting 2128854

I had what I thought was a 69 383 my Dad bought from a friend that was in a 69 road runner that got wrecked and sat in a shed since like 1980 then in 95 I brought it to my house put it in the corner of the shop and there it sat until today .
So on the side a machine shop put a plate with rebuild data .
I looked at the casting numbers and it looks to be cast 9-6-60 ?
And is 2128854-5 and below says LL
The machine shop also stamped something on the front pad .
So I can't mind much info on this motor ?
What I find leads me to 1964 ?
Anyone know Therese old big blocks that might be able to shed light ?
Is it worth keeping ?
Thanks
Jim