Those adapters go on the engine side of the carb at the inlet ports. The bolt holes go over the existing studs on the engine, and the rubber part goes on the outlet port of the first gen carburetor. On a Rebel, the inlet adapter between the airbox and the single carb is a slip on rubber part that has a airbox grommet groove that grips the sheetmetal wall of the airbox solidly.
2004 Rebel 250, 2003 BMW K1200GT (roadburner), 2004 BMW R1200GS(all purpose),
1973 Norton Interstate (in a box in the basement)
1968 Triumph Bonneville