Here it is in a nutshell. As long as you're talking same body style - 88-98 (GMT400, or "OBS") - They swap around the same as long as bed length is the same. A dually bed is nothing more than a longbed that has had the sidewalls chopped out for tire clearance, and holes drilled for the dually fender extensions to bolt up.
What you will find is that a Topkick, being a medium duty truck, has nothing in common framerail wise with regular pickups. The wheelbase is different and the frame rails are straight instead of tapered, flat instead of having any kind of upkick past the rear of the cab, and are narrower - typically on 34" centers as an industry standard for aftermarket work beds.
Wheelbases on the medium duty trucks tend to be 4" longer from the start - for example a regular cab longbed would be 131.5" wheelbase; a medium duty shorty truck would be 135.5". Then they add 2' for the next size, 159.5", 2' more for 183.5", etc.
It can be done, and has been many times, just takes some fab work. Find out your wheelbase (will be printed on the SPID label inside the glovebox with your RPO codes) and go from there. You'll either be adding some length to the bed, making something to fill the gap, or shortening the frame/driveshaft/etc. all of which have been done. You'll also be making your own bed mounts.
If it were a 3500HD the dually bed would be too wide as the cab & chassis rear end is 8" narrower than a regular 1 ton dually rear; I've seen some people take a non-dually longbed and add flares to it instead of dually fenders. Looks goofy but is the correct width. You might say to yourself, "I could narrow the bed" but then it would be narrower than the body, and look like a stepside. My plan for one would be to narrow the dually flares instead, 4" each, not easy but do-able - and then widen the wheel tubs inside the bed for clearance. Your Kodiak rear end may be wider so this may not be an issue; dunno.
Did I blabber on long enough for ya?