Reading another forum about the Burlen system which at the moment covers some SU Carbs I saw mention of another company
Classic Car Fuel Injection Conversion - Convert to Fuel Injection - Improved Starting, Running, Performance and Fuel Economy they actually list Bristol as one of the makes they can supply kits for but as they cater for american cars as well including Chrysler this may be for the later V8 cars.
I think if we do anything with my 403 later this year, head off awaiting repair at the moment, I might investigate this a bit further, not for the 401 as I had the parts to hand to replace the worn component.
Burlen can supply service parts for the carbs on a Bristol and I think still offer an overhaul service.