Looking for a cap, what fits?

I am currently searching for a cap for my truck, 2008 4x4 base model with the regular cap. I have a 6ft bed, but I don't know the exact dimensions. Was wondering if certain caps are designed to only fit certain makes/models? Or will they still fit as long as the dimensions are the same? The one I found locally is from an S10
Trying to find a used one because I don't have the dough for a brand new one.
chevy https://elmira.craigslist.org/pts/d/leer-truck-cap/6497610581.html

 

Not sure where you are on this, I have been wondering and researching the same thing. It appears they pretty truck specific. I did find this chart.

https://raybuck.com/pickup-truck-bed-size-dimensions/

 

That is helpful, thank you. Still on the hunt for one that doesn't break the bank

 

LOL, I feel ya. I have found several good deals on your size bed, but not the short box

 

Keep in mind that the shell for the regular cab is specific to the regular cab. The angle of the rear of the cab is different from the access cab and the double cab long bead. A shell form those trucks will fit, but you have to slide the shell towards the rear about an inch to keep from hitting the 3rd brake light...and the angle looks "off" when using a shell from those trucks.