The best way to determine the answer is to mount every thing with your current bottom bracket, take measurements, and calculate how many mm you need to move your chain ring. Subtract (usually you will be moving your crank inward) this from your current spindle length to get a specification for a new spindle or cartridge bottom bracket. If you do not have a bottom bracket at this time, you can take a guess, buy a cheap (i.e don't invest a lot of money at this point) BB unit and hope that it works. If not, you can use it to do the calculation above to then buy the right length.

Good luck.