Mostly agree with Mike800, except the BDX specs are too vague, only fitting certain years and models. I believe you should assemble your DD with the proper bearing and measure your axial free play at your DD output shaft, using a dial indicator (ebay, Harbor Freight, $30). With a replacement SKF 3203 bearing installed, my 2011 HCR had 0.012" axial clearance, and thus no need to trim the DD transfer shaft. Have not measured my 2009 M8 axial clearance.
With your DD out of the machine and the wider bearing installed, if your DD cover won't close without forcing it, you need to machine your DD transfer shaft to allow room for the wider 5203/3203 bearing and some axial clearance. You should measure the gap around the edge of your DD cover using feeler gages and add 0.005" to 0.010" for axial clearance. Then have your transfer shaft machined accordingly. Cost me $50 at a local precision grinding shop to cut down my 2009 M8 transfer shaft.
My 2011 HCR DD transfer shaft was fine as-is, and my track drive shaft was way too-long and/or my tunnel way too-narrow. My HCR drive shaft needed to be trimmed 0.150" (0.115" on the brake side shoulder and 0.035 on the DD end - to center the drivers). I had it machined 0.130" total, thinking that was enough, based on my best measurements. Turned out it wasn't enough, but much better than it was from the factory. I also made room for the missing brake-side bearing shield.
If your track drive shaft is NOT too long, you don't need to machine it. You can measure with a dial indicator on the outside of your DD, before and after you loosen it. Or you can measure with a steel bar and feeler gages on the inside of your tunnel. See
http://www.snowestonline.com/forum/showthread.php?p=3019754#post3019754 for details.
Good Luck !!
