I have done this very conversion several times. I don't know of anybody that makes the adapters you would need for the rear and if you have them custom made they will be ridiculous in price I'm sure. The way I have always done it is to buy the correct dually rear end for your year truck. You can find good used ones on eBay, craigslist or your local salvage yard. The switch out is easy and then you can sell your old SRW axle. I have sold the SRW axle for close to the same as I bought the DRW axle for. Very cost effective. Just make sure the ratio is the same on the DRW as in your old axle as to not cause problems with the 4x4.