My experience with replacement and reached springs is not good. My BJ8P1 has the same rear suspension as your BJ7 but due to the transverse resonator installed on the BJ8, clearance was important as clearance had dropped to around 2" and commonly crapped on any incline. I initially had the original springs reached locally which proved a short time solution. As an alternative, I purchased new replacement springs and they too proved only a short time solution. In both actions, the springs raised my Healey's rear quite high but soon settled and then fell below where the originals had been before any action had been taken.
As a result, I decided to try and add an extra long (second) leaf as mentioned by another Forum member (I don't remember who)). Since the original spring set seemed more substantial then the purchased replacements (yes, I saved the old set), I took the second leafs from the purchased replacements and added them to the original sets and installed them on the car.
The result was, and is still, very satisfying. It is very difficult to feel any additional stiffness as the ride is no harsher and remains very comfortable. Additionally, the car now provides at least 3 inches of clearance below the resonator and does not dip or scrape on small inclines (i.e. driveways, etc.) or road dips.
Good luck,
Ray (64BJ8P1)