I kept seeing that fuel pump picture as a canister style electric pump. The blue conduit on the line next to is is what Ford uses on their diesel fuel systems and we have it on some of our gasoline powered vans. Sheesh...
You should use flexible line (hose) between the engine and steel line attached to the frame and also between the cab/tank and the steel line on the frame. Typically these hose sections are less than 6" long.
The brass fitting you are holding in your hand in the newest pictures is 3/8" inverted flare female. It is not really the correct match for the brass fitting in the pump. I would remove the brass fitting in the pump and check for a 1/4" pipe fitting. If the pump is 1/4" pipe I would use a 1/4" pipe to hose barb fitting to simplify the connection.
At the tank I would probably use a 3/8" pipe male to 1/4" pipe female bushing. Then I would use a 1/4" pipe to hose barb fitting just like at the pump. It is possible to find 3/8" pipe to hose barb but in this are it's tricky so the 1/4" pipe would be easier.
The ends of the steel tube on the frame should be flared slightly or bubbled to prevent the rubber hoses from coming off as easily. The frame line is a suction line so you could attach the hoses without a bubble and it would probably work ok but I'd make sure the bubble was there.
Good luck.