If you can verify with someone to find out if F12/14 are the same as F20 shutter controls...I do have some fairly closeup pictures of an F20 showing the control part where it would attach under your gas tank strap and also of the end up by the actual shutter too. I CAN POST THE F20 PICS IF THAT WOULD BE HELPFUL. They are pics from a rusty F20 I saw on auction.
Will also go check my junkyard pics to see if I can find an F12 or F14 with one on it. Todd Markles book shows about 5 pics of 12s or 14s - but not close up enought to show details.