Hello. I have been working on cars and light trucks for over 45 years. Last week-end I was helping a friend clean his new residence's barn and we found what we believe to be a chevy 283 with a 2bbl carb, not too odd; but this one has what appears to be a factory installed diaphram, hard piped into an auxilary vacumm line to the base of the distributor. I have asked locally, but no one seems to have knowledge of this set-up. Can anyone out there enlighten me? Thanks!