I have a 12" Dagor Gold rim serial# 772802 and there are some markings etched on the rim of the rear element.
I use this lens for 2:1 portraits on my Wisner 12x20. And some landscapes, but it barely covers.
"EF 302.7"
"BF278.4"
"ND 5.95"

What do these mean?

"EF 302,7" I am guessing might be the effective focal length?