dont do it that way... dont anyone take this the wrong way, but what are you mexian? (thats an expression we use when you see **** like that down here in houston... curb feelers, wings on trucks, tires that stick out past the fender, every concieveable accessory on a P.O.S.) anyway do it the right way and narrow the rear axel. you might have already thought about that, but its gona be hella cheaper than 2 bedsides. if you go new, geeze i work at a dealership and reg. bed stepside panels (MY COST is) 550.. plus paint, plus wheels and tires.
heres what im going to do to my 87.. and it can be done to your style too.
find the correct offset wheel or buy a wheel that you like and thats wide enough probally 15x15
narrow the axel to fit the new wheel/tire combo
either 4 link the rear end or box in the frame rail and flip the leaf spring hangers to the inside of the frame. and lastly get a 2nd set of inner fenderss (for the bed) cut
weld 2 of them together to achieve a factory wheel hump. if the wheel travel wille exceed the stock wheel well, they make aftermaket wheel wells. not only will it have the baller status, you wont have an extra foot of truck hangin on each side of your truck. just an alternative to your idea. on a side note, i seen a video on streetfire of a dodge dulley with a huge slick (just like you guys are talking about) and looked cool.. it ran a 13.x or better...
different strokes for different folks
clint

 

its gonna be cheaper to get a used dually bed than to get a narrowed rear end and 4link the rear and custom cut some fenders.

 

I'd go with a used bed for sure. I like the look of duallys plus I can do all the work myself. Plus if I four link the rear, I'd want air bags and then I'd have to do the front also, then it's getting exspensive.