Help ID brake booster
 

I have a Delco Moraine stamped booster, the stamp is right side up. On one tab front side has 109 which I think is Julian date. On the same tab back side is 851 stamped. There are no markings on the rod, and a raised T on the plastic cover were the rod comes out of booster. Any help would be appreciated.

Could that 851 really be 391?

It is most likely a 8 maybe a 9, but I don't think so. It looks like a faint 2 at the end so maybe 8512.