1973 Dart Sport 340 period correct Tach
I think Sun were lately made by Sunpro. Here's a little info from Summit:
Sunpro began manufacturing industrial tachometers for Jeeps and tanks in 1935 and evolved into one of hot rodding’s most well-known suppliers of tachs and gauges. The iconic Sun Super Tach could be found inside cars at dragstrips across the country during the 1960s and quickly became one of the most popular tachometers by 1970. Sunpro has since expanded its product line to include a variety of gauge styles and became the first company to offer its tachs and gauges with color dial faces, lighted pointers, and chrome bezels. You’ll find a huge selection of Sunpro tachometers, gauges, and gauge installation accessories at Summit Racing—shop now!