Be Careful
Congratulations on restoring your original member ID!
I knew people who had that same late '80s model, and they were on a first name basis with the Sub Zero repairman.
Like Tom said, with any counter depth refrigerator, you're going to sacrifice capacity, but depending on the model, your '63 Combination could have counter depth dimensions too. In that case, the Sub Zero would probably offer a little more capacity.
Tom is also correct about the freezer. It's small and difficult to access. IIRC, it has a door instead of a drawer, so it's a real PITA to find anything in it.