Went through this a few years ago. Had an older Sun tach I wanted to use with MSD. It wasn't the older ones with the sender box,,just a late '60's early '70's one piece. I bought the tach adapter from MSD and it worked fine. The adapter was about $80-90. I looked at Sun's web page and found they make a tach that looks 'retro' that will plug right into the MSD box. Don't remember the exact price, but wasn't real bad.