They aren’t commonly interchangeable as the two mounting bolts are further aside around the Blacktop trumpets. Please see “Throttle bodies” for more information. Also the opening from the Blacktop inlet ports are close to four to 5mm wider at their entrance above the Silvertop providing a bigger cross sectional region. https://4age-20v44679.designertoblog.com/63574669/4age-20v-no-further-a-mystery