Anyone want to talk about descant horns?
I was thinking of converting a pre-letter Conn 8D into a descant. It would require adding Merewether type valve and separate tubing for the lead pipes and bell branches.

Anybody done anything like this?
Pros/Cons?

Would that make it a Conn 8D triple? That would be a first, for sure.

No, it would not make it a triple, although that is another way to go. When you add or put on the high F set of valves you can't use the same leadpipe length or first bell branch.
I don't like triples. I have not been happy with any that I have played (schmid, paxman, etc). There is something about the weight of the horn and mass that I feel affects the high horn harmonics negatively.

<Added>

I am thinking of trying to get that real large sound in the upper range above c. Because of bore and taper most high f horns get a lighter sound. I was thinking of going full bore large sound. Perhaps it is not possible and that is why it hasn't been done.

Nothing is ever impossible. It may be improbable, but everything is possible no matter what.