I have a 1973 Perkins 4.107 Diesel engine. Kind of the Great great grandfather to your Perkins Prema 50. The flex hoses used by Perkins are standard fuel lines on the return system and the tank to engine systems. The high pressure lines that transfer fuel from the high pressure pump to the injectors are specifically designed and would be sourced from Perkins.
I sourced my lines from a local hose & hydraulic shop that serves the truck industry. I took the hoses for my fuel lines from the manifold to the primary fuel filter, the primary fuel filter to the engine, and the return lines to the shop. In about an hour they had made duplicates. Cost was about $120 for 6 fuel lines and threaded connectors cut to length and ready for assembly.
I suspect you can source the parts and make up the lines for less, use a hydraulic shop that has all the pieces and parts or contact the local Perkins distributor purchase premade and Perkins numbered hoses for your engine.
Your choice.
