Trunk Lid Hinge Arm - This post was originally part of a larger thread that included six different running changes so choose to separate out each to reduce the clutter
In the survey the highest San Jose sequential numbered example with the double thickness/reinforced trunk spring arm was - 5R09K173xxx
The lowest sequential number example with the driver's side trunk hinge without the extra reinforcement was - 5R09C1800xx.
A difference of about 7,000 unit numbers most of them being unrelated (to the subject) coupes.
Timeline suggests that the change over likely took place during the month of January 1965 at San Jose