I think your weight estimate is high. My bet is 3400+/-. I use 125# on my ladder bar 64 Belvedere. Car weighs 3340 ready to race. The rear weighs 1536. The unsprung weight is 330#. Shocks are mounted behind the rear axle. 125/130 will be very close. If you have a lot of power or run on drag radials you may want to go to 150 for less stored energy as you may not need as much "hit". For the record mine makes around 875hp.
Doug