It used to not be that way. I've got a Hydrabed model 250 (predecessor to the 3250) on my old '96 F350 C&C and it fits perfect, didn't even have to trim the frame. I wanted the same bed on my new truck a few years back, as the 3350 would hit the frame on a few of our trailers. So I went and measured a few of the new Ford C&C trucks and there would have been a huge gap between the headboard and rear of the cab if a 3250 was installed. The fuel tank was shoved up so close to the back of the frame rails that there was no available frame to trim off behind the rear gusset, also. For that reason, I wound up ordering a dually pickup and removing the bed once I got it home and selling the bed. I actually called Hydrabed a few times before ordering the truck and had them spec out the truck to work best with their bed, very helpful folks. They even called me about 6 months after installing the bed to see how I liked it, and the changes they have made since my last bed. How many companies would do that in today's world?
To the original poster:
Trucks from the factory with an 8' bed or a "bed delete": 56" cab to axle.
Cab and Chassis trucks: 60" cab to axle, or 84" for the longer (11'+)beds
C&C trucks usually have narrower/straight frame rails. Used to be 33" wide for C&C vs. 37" wide for pickups, not sure if that still holds true. My '19 F350 has 42" frame rails for what it's worth.
If your Chevy came with a factory pickup bed on it, the simplest thing for you to do is to buy another single wheel truck with an 8' bed on it and remove the bed to sell/store. The old bed will need some fabricating done to make it fit the new truck, as far as mounting to the frame attachment points. Be aware that some of the newer trucks will not function properly if you remove the bed and try to operate without the taillights plugged in. My Ford basically shut down the computer until I found out what was going on and hooked up the taillights. I've heard that some other mfg's (Dodge in particular) can sustain damage to the computer if operated without the lights. That being said, I'd take it somewhere that's familiar with the procedure unless you're handy enough to do it yourself.
Best of luck.