If you are running on a tight carpet track, put 500,000wt in it. If running outdoors, id start with 250,000wt or 200,000wt. You should be in the ball park if you use these oil weights. Build the diff as instructed, no special ways to build it. But make sure you pick up a set of the bearings you need, to fit it in your 05. I seriously love these diffs, IMHO these are the best diff for a M chassis bare none. Now if your running an 03, your out of luck as these wont fit without modifications to the chassis halves.

This is the diff here
Note the mention of the required bearings.....