I'm about to buy a new repro tach for my 67 and have an HEI ignition. I had read several threads about problems with original tachs either not working at all or needing some kind of filter to work. Are you sure the aftermarket repro tachs will work as is with an HEI ? If so that's great news.Do a search. Also in the elec. basics sticky Jim has shown how to make a simple filter. My 69 did not have an original tach when I bought the car. I did a search about installing one in place of the original fuel gauge. What I found was that some that hooked up their original stock tach to a HEI ingnition was that it messed it up. But, that by using the new aftermarket stock type tachs it was not an issue. That is what I used and have not had an issue. So I wouldn't want you to mess up your original tach. They aren't cheap IMO. I am running the MSD large cap HEI dist.