The interior changeover on the rear opening as observed for the rear flange casting from the throttle housing is different. The Silvertops have an easy spherical machined opening at the identical 43mm diameter with the blade / throttle Heart bore while the Blacktop has far more of the kidney form https://jaredabbzw.thekatyblog.com/30226327/rumored-buzz-on-jdm-toyota-4a-ge