Originally Posted by Slash5

I'd try the crank without the spacer first. The Shimano crank must have a longer spindle for the triple and therefore needs the spacer. The FSA may not. The spacer will be available at any LBS - MTB BBs come with several and it's the same spacer as used on freehubs. If the FSA crank has too much clearance so moves side to side or the chainring touches the chainstay you will have to add spacers to the drive side. You could stack 1mm spacers side to side for maximum adjustability.
However I have not had luck with using Shimano BBs with FSA cranksets. The FSA crankset is too tight. They are both 24mm spindles but with different tolerances. It may work for you.