how to slightly lift '65 barracuda tail end

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

Your springs are shot out.
Stock replacement springs will raise the car back up to where it should be.
I wouldn't recommend a +1" spring. Ive seen it many times where people weren't happy with
how high the *** end ended up. Go stock replacement.

ESPO is a great company. and has everything you will need for the replacement. Very fair pricing as well.
I would replace the rear shackle bushings while your at it.