Hi Rob,
I too used a service that would spin balance the wheel on the car. The balancer did a good job of balancing wheel, tire, and drum as a single unit but required all components be maintain in the same alignment. Tire rotation was something you could not do and many non-Healey owners, not plagued with unbalanced drums (I had never heard of then), preferred the flexibility to rotate their tires for extended longevity.
All the best,
Ray(64BJ8P1)