We are trying to install a vacuum advance in the MGA; it was not installed by the mechanic who worked on the car prior to when I took possession of the car in 2016. I do not know if it was present when the car last ran in the '70s. We have the new part. Does anyone know the size of the threads on the carb so that we can buy a tap to clean them? We have been told this can be somewhat difficult to install and we want to be sure we don't cross-thread the new part or carb.