well, I’d imagine your current springs are 50 years olds?
do you want it 1” lower than what you have now.
Tire diameter effects height too.
what tire do you have now? And what is the measurement to the top of the rear fender lip?
mine is 24 5/16” to top of lip on my 1968 barracuda that has same lip as you. That’s with a 24.6” diameter tire (12.3 radius)
if I had 245/45/17 tire my lip would be .55” ~ 1/2” higher to make it 24 13/16” to top of lip
View attachment 1715688168