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What sparking plug are you intending to use? It looks a bit tight between the valves and the plug. You will also need a special socket to fit and remove the plugs like on the Triumph Dolomite Sprint.
What fuel and ignition systems are you planning for Halfa? Yours I think would have had twin 45 DCOE Webers and a couple of years later they went to Spica mechanical fuel injection. Both could be a challenge