This is Original Primary with the Halo Ring. Updated Primary is now made with out the Halo Ring and has Stronger Cam Plate and Bushings. Now on most 2021 and Up models. (see part # 21300-004-1000). $215 vs $260- Out of stock
This 500 Cylinder Head is For the Carburetor Models and the EFI engines that has the 1-Wire Temp Switch and 2-Prong Temp Sensor that is not used on the Carburetor models.Mainly for the Bucket Seat Models. 
This solves the High Compression problem when the Weights open too soon when just cranking it over to start.This is for (2) Springs.
