FSA Mega Exo has its own BB concept and it comes fully attached to the drive side crank. Consider it "1 Piece". All the ones I have seen (and use with considerable delight) are triples not singles, but who knows...
Overall the FSA Mega Exo gives me all the impression of being an excellent crank and one that can occasionally be found at a killer price (~$79 complete kit about a year back at Nashbar for the last couple I bought) so be sure to shop for price if buying another. Should be findable in 170, 175, and 177.5mm (I remember having difficulty finding one in 180mm and took the closest available to that). The ones I have came with a spacer to use as needed/if needed on left or right side to optimize the chain line, but I never found it was needed (for 9 speed).
Hope that helps
/K