GXP Bottom Bracket - Spacers?

Greetings MTBers,

I'm planning to fit a set of Truvativ Cranks to my 2007 Marin Attack Trail frame.

The frame measures 68mm across the section which hosts the Bottom Bracket (BB).

I've got a GXP Bottom Bracket, which I believe will fit.

I don't have any manuals but found this on the internet - http://www.sram.com/sites/default/files ... nksets.pdf

Sorry if this is a dumb question but do I need to fit any Spacers on the inside of the BB bearing cups please? If so, how many? What size and which side|(s)?

I think this answer is: One 2.5mm Spacer to be fitted on both sides of the BB. However, the BB didn't come with any Spacers so I was thinking of using two (of the three) that came off the old FSA Bottom Bracket - They are each 2.5mm wide.

Any advice from an expert would be most welcome.

Thanks in advance and Season's Greetings!