Did some thinking: Realized that the appropriate mechanism to
express that A and B are two ways of representing the same thing
is to do so via opCast. I had not considered this option
carefully initially as I am translating someone else's C++ code
to D and hoped that they had used the appropriate representations
on the C++ side.
I added the appropriate code to permit casting and I was then
able to get the desired code-reuse and template constraints.
Accordingly, I no longer need an answer to my second question
unless someone knows of a more idiomatic way to get the same
results.
