how to slightly lift '65 barracuda tail end

Johnny Dart said
You never mentioned anything about your existing springs.
Are they the original springs ? If they are older springs, they are sagging.
Get yourself a set of stock replacement springs from ESPO.
That will bring the rear back up to your liking.

Very good point, they are older, maybe original. Currently the quarter panel lip is 22" off the ground. I will check out the pricing.