Need some help selecting coil overs for rear of 1972 firebird

[j99fbody]

Im in the process of building a torque arm style rear suspension for my 1972 firebird and going to use adjustable coil overs but not sure on what lb spring and shock length would work well on the car.

[marolf101x]

You want 5" of travel at the wheels. Shock stroke depends on how and where you have the shocks mounted.

Use this to figure spring rate:
http://www.ridetech.com/tech/spring-rate-calculator/

[j99fbody]

thanks!