FWIW, I would use lead where I could on your nice old shotgun. Hevi-Shot is NOT as soft as lead- it is a Tungsten-Nickel-Iron alloy. However, why not contact Remington, and maybe ask them about their Wingmaster ammo? It is also a non-toxic shot that is about 16% softer than Hevi-Shot.
What we have here is... failure- to communicate.