I am doing a frame off on my 70 Cutlass SX Convertible. I bought new front springs that have the flat spot on one end and rounded coil on the other and understand and they only go in one way (flat spot up top I think). Anyway, the old springs which look original are about 1 inch longer than my new ones and have no flat spot - they look the same on both ends. I don't think they were ever replaced - but don;t know. Were GM's original springs like this, or were they replaced along the way sometime? Reason I ask is because when I googled springs for 70 Cutlass, a Moog pic came up (for an auto parts store) showing springs for a 70 Cutlass with round coils on both sides - no flat spot and I know Moog supplied many suspension parts when these cars were new.

 

Every 64-72 A-body front end I've ever rebuilt had the flat coil on top and the full coil on the bottom. Note that the spring pocket in the lower control arm is contoured for this full coil. The height of the spring by itself won't tell you anything. You need to know both the height and the spring rate. For example, a stiffer spring rate usually requires a shorter unloaded spring length to achieve the same ride height.