[Tony Smith]

The Lucas distributor is basically the same firing order as the US/Canadian Crab dizzy. On other 21 stud engines with the Diver's Helmet distributor, all leads for the plugs on the left bank of cylinders come off the left cap, and all leads for the right bank come off the right cap, none cross over. With the Crab cap comes a trap for the uninitiated. Lead for No 3 Cyl is on the left bank of the cap and No 5 cyl is on the right side of the cap. The ignition leads run through their conduits and come out the inner side and cross over the inlet manifold. I can't see the leads crossing over in your pic, Bryan.
The following pic may assist:
PS Regarding the lack of timing marks, take all the plugs out except No1, remove the cap on the dizzy and turn the crank pulley. You should be getting compression somewhere when the rotor arm is near the 9 to 10 o'clock position. That will let you know if the Distributor is in phase or 180deg out.