I have a clawfoot tub which has an unusually large spread of 11" between the hot and cold holes. The holes are in the deck of the tub, and there is also a larger mystery hole in the center between those two holes. I need all the hardware (faucet, drain, shower, enclosure) for this tub. I'd like to have a stand up type shower, but I can't find a fixture to accommodate this wide center spread, nor to utilise the big hole in the middle. I was thinking about perhaps a wideset faucet set with a diverter in the top of the faucet to attach a riser for the shower, but I can't find anything like this. HELP!

You would probably need to go with individual deck mounted faucets that can be adjusted with chrome pipes. Many have shower arms. Google "deck mounted faucets" for examples. Many have adjustable spreads to 12".

Check out this adjustable deck mount clawfoot tub faucet... can accommodate up to a 12" spread:

Water Creation F6-0004-0 Vintage Classic Adjustable Center Deck Mount Tub Faucet with Handheld Shower - Fixture Universe

Scroll down the page to confirm adjustable spread from 4-12". The faucet even has a hand-held shower!

You can plug the unused center hole with a "sink hole cover".

Mark