Lister D shaft drive magneto timing

Hi everyone,
This is my first post to the forum so please forgive me if this question has been asked before.
I am in the process of recommissioning an early Lister D for pumping duties. Amongst other tasks, I have had to repair the magneto which is a Wipac A type. The engine is now running, but it's rough and lacking power; I'm pretty sure the ignition timing is out.
The question now is how do I adjust/set up the ignition timing? Everywhere I have looked are the instructions for the later chain driven type magneto but I have the early shaft drive and I can neither find instructions nor figure it out just looking at it! And there is a large amount of backlash in the magneto coupling which makes me wonder if a part is missing or its very hit and miss (so to speak!) anyway.
Any advise from anyone who knows about the shaft drive versions would be appreciated!
Thank you,
Andrew

OK, so now I can answer my own post!
The answers is that there is no adjustment for the timing on the shaft drive engines! There is a numbered collar/coupling ring on the drive from the bevel gear which meshes with the magneto and I suspect there once were variants of that coupling ring to modify the timing. But I only have the one.
What I discovered was that the valve timing was out, and so the ignition timing was out also, and the head gasket was leaking. A bad attempt at a rebuild by a previous owner!
I have set the valve timing up correctly and fitted a new head gasket with blue Hylomar, and all is now well, the engine pulls a good load and runs smoothly.
Fixed!

Got to say Andrew its always a good day when you pose a question and then answer it yourself! - Happy days and a good solution found.

Welcome to the Forum!

Best

Hamish