Adapted a Holley 500 cfm just fine. Save the washers and fine thread bolts and throw the rest of the hardware out if you are keeping the cast iron riser. Use 3" x5/16 allen head to go thru adapter and riser. Nuts given are not fine thread either so you need those. Again this is the V12 so the riser has the equalizer between manifolds. Regular V6 may not have the 2" riser.... Still will have the nut problem.
Nice product especially if your replacing an old Holley 2210 or Carter. The manifold holes need to be elongated to fit the Big 2 barrel manifolds but works well. The finish isnt smooth anymore and helps seal the gaskets.