Interesting, when building the 280ZX and after discussions with the custom suspension builder, I settled on 400F, 300R. Thats wheel rate, car does not have the original type rear suspension. Subsequent circuit driving experience has confirmed that choice.
So, to keep on topic, with that sort of setup and with no rear ARB and a helical/torsen LSD, we should end up with a car down a bit on mid corner speed but up in the corner entry and exit areas?