Since you are downgrading the load capacity at the rear you might replace the front axle with a 1/2-ton type and then use one of the 5-lug or 6-lug conversion kits available.
If you want to maintain your load capacity you'll want to use a bigger rear than the 12-bolt or 9-inch and the 1/2-ton front would be the wrong answer.
Last edited by OldSub; 10/01/2010 2:11 AM. Reason: corrected typo