Rear coil over questions

[touring63]

I am looking for some advice on my 63 nova project. The rear is a nine inch with a three link and a watts link. Currently the top shock mount bar is not mounted. I am looking to purchase them now and don't know what I should go with. Is a taller or shorter shock better? What spring rate to go with? I am not sure of the weight currently but I would like a good starting point. The floor will have to be built so I can mount the upper mounts at almost any height. I am thinking some brand of single adjustable coilover maybe ridetech? Or qa1? The car will be just a low, big wheeled, big braked, mean street car no track days planned. Any opinions would be great.
Thanks in advance.