I've heard that if you just put dually rims on a SRW axle that they will hit the springs. I have yet to see anyone verify this though.
Garrett (Cat_Rebel) did verify this a month or two back when he tried installing dual wheels on his SRW axle in an attempt to create a 7ft-wide rear end (factory SRW is 6ft, factory dually is almost 8ft) to match his 7ft-wide flat bed.
To the OP - is your truck a 2wd or 4x4? 2wd are a piece of cake to convert into duallies, all you'll need is the dually rear axle, the dually front hubs and rotors, and all 6 dually wheels. The complication with the 4x4 comes in from that you have to use D60 front hub extenders to run the dished wheels on the D50 axle, and those extenders seem hard to come across. There are of course kits that you can buy, with spacers that bolt onto your current single wheels (both front and rear) and that you bolt the dually wheels onto, but those can get pretty expensive. Actually the front adapters from these kits can be a good alternative to the hard-to-find D60 hub extenders, a pair of real nice steel ones made by Arrowcraft in MI will cost you about $350. I'd go with a factory dually axle in the rear either way tho. Then you'll have to do something about the bed, you can bolt on factory dually fenders, or you can make your own ones from say diamond-plated aluminum, but you gotta have something to cover those outboard dual wheels as they will be sticking outside your bed.