Mine transition from side at the rear to top at the front where they're out of the way of clutch linkage & away from the driver's side exhaust before it crosses under to the Pass side. I also routed it to come up the rear of the engine since there will be no mech. fuel pump (Exploder front dress).
I'm a believer in as few connections as possible, but I always make the transition from frame to anything else with a flexible line, and at least one of those connections is mounted solid. This the tab on the frame at the engine:
Additionally they're color-coded. Black is the return, Blue is the supply. Those caps were temporary to keep the lines clean. And yes, that is nylon tubing. On purpose. I used Push-to-Connect 'wash-down' fittings for their viton o-ring seals on the tubing. The flexible connection to the engine is Emissions Barrier Fuel Hose used with Push-Lok/Barb-tite hose ends for a complete fuel system with only one hose clamp (& it goes away when I change the fuel tank!).
Low pressure pump and primary fuel filter:
I really need to get back to work on that truck!