If your carb has a boss here, but no screw, it is possible to drill and tap one existing carburetor to accept the HAC vac nipple
Intersecting holes are .115 ± inches diameter. The top portion of the horizontal hole is drilled and tapped to accept a 6 mm diameter x 1 pitch threaded nipple. Hose size is 3/16" ID
Note, when drilling intersecting holes, the vertical (more or less) hole shown here is not at a right angle to the horizontal
A standard plug is peened in place to seal this hole which results from drilling access.