I've got the KYB from Rockauto on back of my 65 GP, they are a bit stiff but do alright.
About 19" eye to eye installed with ESPO standard coils that have been under there at least 10 years, car sits mostly level. According to Rock, the KYBs extend to nearly 22". How high is the center of your rear wheel opening directly above center of rear wheel? My GP is roughly 9".
https://www.rockauto.com/en/moreinfo...t=7556&jsn=419