You could probably get away with it if the clams were very close to the PCs... I mean, they would probably survive for a while at least (EDIT: given good quality, regularly changed bulbs
), though long term would be iffy (stronger light = stronger clam, better able to ride out situations that would do a weak clam in). There are some SPS that have done well under PCs, though your selection would be pretty limited (and they would do better under stronger light). A T. squamosa might be alright really close to the PCs (like a few inches) but for sure not croceas or maximas.
T5 would definitely be a better choice in a tank that deep, PCs don't penetrate depth very well at all.
I plan to refurbish my current 10 gallon reef into a 10 gallon single clam tank later this year. I've been pretty smitten with them since I signed up on Canreef and the tank is coming to the age where I can start to consider it.