you could keep T. derasa, T. squamosa, or H. hippopus on the substrate or a gold T. maxima high up in the rockwork, but you don't have enuff light for T.crocea or the maxima "ultras". you could probably swing a gold-centered T. maxima high in the rockwork as well.
i'd get a 3" specimen of whatever you get, as babies (<2.5") are a lot more touchy than established specimens. also, i recommend feeding the clams live phytoplankton a couple of times a week. also, clams hate water shifts and don't do well at high temps (keep them below 80*F). make sure your Ca level is 450-475 ppm.
HTH