Newbie kinda question. I have a B&J 8x10. The lens on it reads: 8x10 Turner Reich ANAST F6 8 SER II 213667 Grundlach Manufacturing Corp.

On the aperture ring is reads 12 "

on the inside element it reads 21 "

Can anyone help me to identify the focal length? Also, it's shutter is the pneumatic rubber ball. Is it possible to put a variable speed shutter on this thing?

Thanks, and sorry for the cluelessness.