I have fitted a Winterburn capacitor discharge ignition system to several of my cars including my 401 and plug problems are a thing of the past, I am not keen on working on car electrics but have had no problems installing the systems myself. The control unit allows the option to run in standard or cd mode as well as switching the system off which can be used as an immobiliser.
Also no adjustments to timing are needed, no awkward modifications to your distributor which could leave you stranded by the side of the road if alternative systems fail though you may have to reduce idle speed in CD mode due to the more efficient fuel burn, on an S2 Bentley I got about an extra 2 mpg , significant on a car doing about 14/15 mpg.
Geoff.
http://www.capacitordischargeignition.com/
P.S. NGK recommend the CR7 HS plugs for the 401 and 403 which is what I have in my 401.