For those asking, here are the hearings I used:
For the front of the slide: McGill CF 1 3/8 S that's a 1 3/8 diameter cam follower.
You can probably find cheaper, but here is a link: https://www.motion.com/products/sku/0...

For the roller mounted to the truck, near the tailgate, I'd recommend a 1" or even a 3/4" cam yoke roller, like the McGill CYR 1 S. I used a 1.5", because I had them around but you'll get a lower deck height with a smaller diameter.
https://www.motion.com/products/sku/0...