From the pump back an OEM configuration switches between hose and hard line a couple of times. First, a 5/16" hose section connects to the pump and to 5/16" steel line on the frame. IIRC this hose has 5/16" inverted flare female fittings crimped to both ends. Next, the 5/16" steel line extends down the frame rail then under the cab and connects to a 5/16" hose section which transitions into the cab. Both ends of the hose are again 5/16" inverted flare female. Next is a short section of 5/16" tube which connects with the 5/16" hose near the floor on one end and connects with the sender at the top of the tank at the other.
You can find the factory assembly manual on trifive.com:
http://www.trifive.com/55-59Assy.pdf
Chapter 8 shows the fuel line and fuel tank details.