whats the size of the factory fuel hard line?

reason for question?
i have a 2000 rcsb silverado 5.3. i had a fuel cell built for it and mounted it behind the axle. what i would like to do instead of running all new fuel line to the engine bay is to just use some Russel compression fittings to connect to the hard line at the cab and run -an line back to the cell. i am at work in SoCal and my truck is in Houston,tx . so im trying to order everything i need so when i go home on the weekends i can have everything together. any help would be greatly appreciated.

 

3/8" supply, 5/16" return.

 

thanks