I agree with Bill re. the slow revs at the magneto position being used to drive an alternator. If one has got rid of the ESA and is using a gear drive rather than chain then there is plenty of depth there to position an alternator. This could either be mounted on the main shaft or, with the aid of a hollow gear, driven at double engine speed. That is the speed at which the Walkernators are driven on twins. A variety of alternators are available from modern bikes, which generally use higher revs than a Vin. Hence the possible need for the hollow gear and increasing the speed of rotation of the alternator. New, or modified, primary drive covers would be needed. John Emmanuel's bike has the alternator from a Guzzi 'V' twin in that position and it is hard to notice it.
Modern car oil pumps have enormous flow rates, particularly for the 8 cylinder engines and one of those working at half engine speed would be more that enough to feed either a standard Vincent lower end or a plain bearing system including mains and big ends.
And a note to vinhrd998; if the helical teeth were ground off the clutch parts shown earlier then a steel gear could be shrunk on over that and then the rest of the clutch used. Note that on the Suzuki that originally used that clutch there was a large gear ratio reduction between the main shaft and the clutch gear. That could not be done on a Vin and so stronger shock absorber springs would be needed to cope with the extra torque.
Nice to see people still trying to improve our bikes.
One other thing to notice on the engine shown in #8 above is the extra depth of the part or the cylinder head housing the valves. I imagine that their valve lift is about double that of a standard Vin.