It should be relatively easy. They've been making SBC C/K headers for these trucks since, well, 1973.
I have a set of $200 Dynomax's that came off my personal SBC (now LS) C10. They sealed fine. There were a set of Jeg's ceramic coated $300 headers on a K10 I did a restoration on with a built 400. They sealed fine. It's not the header for the most part (unless it's an awful, import, $100 set from Amazon or eBay) it's how you install them, and the gaskets you use. Both sets fit fine in the chassis; with only minimal clearance on one tube in the K10. I build ten-ish cars a year as a side hustle for friends, many spend time on a dyno.
Once you reach all-the-gasses-your-motor-can-flow on the exhaust side, there's no additional benefit to be had.
Next; virtually any primary size you select for a 383 (1 5/8, 1 3/4, 1 7/8, 2, 2 1/8) will flow fine. Unless you're building a Bonneville salt flats 220 mph racer, and seeking to eek out the last 2 mph, there will be no measurable difference in performance. For reference, my '69 Corvette currently runs a KaTech built LS7 from a '08 Z06. I have dyno sheets for 719 crank horsepower when I built her. The same people who build the motors for the Pratt and Miller C5/C6/C7/C8 factory prep race cars told me 1 3/4s is the perfect primary for that car. I can and will guarantee she's inhaling and exhaling harder than a Gen1 SBC.
My advice? Query what fits the chassis best. What requires the least amount of 5lb hammer and 50mm socket clearancing to make it in there. You'll never see a difference in streetable horsepower and torque, unless you're speaking of radically different designs (Tri-Y, cast iron Sandersons, shortys, full-tube, etc.)
The LS in my C10? A cam'd, intaked, 5.3? I'm running Ceramic coated Summit/Thorley Tri-Ys. It's a truck. I use it like a truck when I need to do truck things. Torque is king, I'm not aiming for 160mph blasts down the highway. I want to move the trencher I rented for yard work this weekend effortlessly. Even the different design header, it probably shifted the torque curve down a few hundred RPMs, and gave me 5-10 ft/lbs versus a full-length tube header.
Give it a balance pipe (X-preferably, H if it's all your shop can do) before the cats; it'll do more for exhaust gas resonance/standing wave balance (if you don't know what I'm speaking of, I can share engineering data with you), and make the exhaust scavenge better. Get good high-flow cats. Spend your cash there, not on the biggest tube header that'll fit.
This is going to be good.
