The frame isself is the same one they use in the 1ton trucks, but the springs are only 1/2 ton rated.
Since you already have the 8" rear end, just swapping out the springs for the 1ton rated kind will make your truck capable of hauling that amount.
Bit of caution though, they are stiff.

Just a side note, there's a 1ton cab/chassis truck (2wd dually) that's been outfitted as a tow truck in Michigan City, IN.
Fun to see!
I'll see if I can grab a pic at some point.

1986 Pickup extracab longbed "Woody edition"
SAS - 33's, 5.29's, lockright rear.

02 IS300 SportCross - my "DD"
94 2wd v6 extracab
04 Outback Wagon- wife's/family car