My twin runs a modified Ford distributor which, when I got it had, been set up with two sets of points. That way the cam becomes less important as the relationship between spark and piston position is controlled by where the points are mounted rather than the shape of the cam. The cam can easily be converted to single lobe. I assume that the range of advance was set to suit the Vincent engine by restricting the bob weight travel. Potentially easier would be to lock the distributor spindle and drive it with a new ATD.
I replaced the points with a Lumenition Optronics CD system and reintroduced the Ford rotor arm and distributor cap. This has worked well for more than three decades.
For a new system I'd recommend a fixed spindle set up with a solid state retard such as the, now unavailable, Lucas Rita.
I fitted a twin Rita system on a Comet and that would start by hand.
Mistral Engineering have developed its successor, called the MOIRA which will work with the old trigger system. It'll give give full power sparks from 60rpm to 20,000 sparks per minute (should be enough for all except Vibrac). It incorporates a shutoff facility to turn it off if inactive for six seconds but switch back on once triggered saving us from flat batteries or burnt out coils. Standard it is 12v negative earth.