Join us on Facebook: Search for 'ConcoursMustang' Private group!https://www.facebook.com/groups/concoursmustang/Indiana SAAC Fall Classic , French Lick, IN Oct 11-12http://www.insaac.org/SAAC National-Sanctioned Concours Event
IMHO I wouldn't use that mark at this time or suggest it on a 65 or 66 Mustang
There was no trace of a yellow mark like that on the original prop valve on my 9/65 SJ car.