From my vast experience of repairing cars (although very much a dinosaur now!) when dealing with anything petrol related I err on the side of caution. The reason why manufacturers use metal pipes with small lengths of rubber hose at either end is for safety reasons as rubber is more likely to be damaged. Worm drive clips do not seal small bore rubber pipes to my satisfaction so that's why I use petrol pipe clips. I also am very choosy about the rubber hose and would only buy branded hose from a manufacturer like Gates - there is an awful lot of s**t rubber petrol pipe about.
I don't want to put down your efforts but if I were fitting a filter to a R4 that previously didn't have one, I would have retained the metal pipe, cut it as necessary, made a bracket up to hold a Terry clip and then fitted an original type fuel filter sealed at either end with short pieces of top quality hose and petrol pipe clips.
I had an underbonnet fire once that was down to my own stupidity in not doing the job properly by using parts that were not up to the job and routing the pipe in an unsafe manner. Therefore I want to share this so the same thing doesn't happen to you.