I would run both new springs. I don't think 600+ spring pressure will cause any problems as long as you don't idle too long, or set idle rpm too low...

My two cents!

Arnie

67 Cuda 8.48@ 158.7 mph 1.18 60' 2,600 DA(so far...) 70 Super Bee 440 Six Pack 4-speed. 13.2 @ 104 Stock exhaust/Street tires.