Acouple of pics to help visualize ...

Some mounts are flat on the top and bottom. SIGglass-filled mounts are used in pic 1. It's a Saito 82 four stroke. You can see that there is access to the bottom of the mount to add nyloc nuts.

Some mounts are flat on the top and rounded on the bottom making it impossible to add a nyloc nut. These mounts require that you drill a hole then tap it with threads to hold the engine mount bolts.

Some cowls make it impossible to access the bottom of the mount even if the mount is flat on both top and bottom. These also require that the mount be drilled and tapped for the engine mount bolts.

pic 1 - 4-stroke, SIGmount, removable cowl
pic 2 - 4-stroke, Hayes AL60 mount, removable cowl
pic 3/4 - 2-stroke, SIGmount, built up imovable wood cowl