Below is a pic of two dampers.  The one at the low left position is from a 62-64 pickup.  The other is the subject of the questions.   It has marking COA 6316A.  1960 auto?  The COA is 6 1/4 lbs, the truck unit is 7 3/4 lbs.  Can they be considered interchangeable?  Would either work in a 312? 

Of the 10 or more dampers I have had, only this one (COA...) has shown up.

Mike

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.