John,
I purchased new springs for my BJ8 ph1, last year. The new springs were the same length. The old springs were also the same length. I was hoping the new springs would raise the car up an inch. They didn't. As a matter of fact the car sat lower. Turns out the new springs didn't have a "set" between the different leafs, and there was not sufficient arch. I ended up returning the springs and rearching the originals. But to answer your question, both springs should be the same length and have the same arch to begin with. Probably more to the point though is how your car sits with them. Level?? Correct height?? Off the top of my head, I think the measurement from the ground to the bottom of the wheel arch, measured at the center of the wheel/axle should be 27 inches all the way around, somewhat dependent on your tire size. The phase 2 BJ8's sit higher in the rear. It is also true that many/most Healeys don't sit exactly level. That might be from springs that have lost their arch, or that the car is normally driven with just the driver and no passenger, or maybe they came that way from the factory. If you purchase new springs, just be sure they help your situation.