You don´t neeed no Tsubaki chain, get any three row chain, split rollers or not - BUT you weld up that dreaded ESA, latest or earlier type no matter, they don´t work all of them. The cam shape is still not effective for protecting the dynamo and chain rollers. Am I right in my thinking that when a split rollers type chain starts to fail it is in all cases at the central row of rollers due to the mass of the rotor/armature acting on the dynamo sprocket and overloaded by the shocks from the useless ESA ?? So my suggestion alternatively get an Alton with its lower mass of rotor and the chain rollers will survive no problem .
The big Laverdas got same triplex chains, Commandos too, and Laverdas today change chains for two single chains, no middle row anymore as triplex chain supply is a problem. Cheap enough then for binning them in periods.
The postwar Horexes with up to 400 cc and 22 hp - half of a Rapide - got duplex chains with split rollers, no ESA at all on them , see photo below middle chain. I never heared about troubles with chains on them, so engine power will not be the matter with Vincents and their triplex type, just the hopeless ESA effects on the middle row of rollers. So there is the root of the problem that you better address .
Vic
duplex chain Horex surrounded by Vincent triplex types:
Horex 400, no ESA :
two brushless magnet rotors, one Miller armature, a Bosch 3ph alternator rotor: