The pink gear is for the earlier cars that don't have an electric sending unit. The white 23 tooth gear is the one to use. It is actually for 355 but will only read about 5 mph fast with 373.
i was looking at my invoice and the part number for the gear says 17271A. i looked it up on 50resto and it says that was the PN for the pink. i knew something was wrong. i picked my car up yesterday and while drivng around on the highway today i was thinking to myself no way are all these cars doing 90. i was trying to keep up with them. same with driving on city streets. im doing 40 and it feels like 30, everyone passing me. i will call the guy who installed them tomorrow, see what he put in there.
look at this link it should tell you what you need to know scroll down to speedo gears. also if you need a speedo gear go to e-bay you can buy one for about $12