on my 1954 3100 with a Nova rear axle what effect will have it on the ride quality? BTW it is somewhat lowered.
You should never have a rear anti-sway bar without a front one, can be dangerous!
Fit a front bar first, it may be enough for you. Unless you drive a lot of twisty small roads (or do some road racing), I am not sure that adding a rear bar would make much of a difference, really...
As for ride quality, it will not make any difference.