Use the largest sheet metal screw (not a wood screw) that fits through the hole in the engine's mounting flange.

A Phillips head instead of a Slotted head screw is a preferred choice for this application IMO(Along with a #2 Phillips screwdriver with a tip that's in good condition).

Bring both mounts up to, but not touching, the crankcase. ANY clearance is good, and better than none.

Hold the engine firmly to the mount, and mark the hole locations. A "scribe" can be made from bar stock or old piece of pushrod with a sharpened tip. Then, you can etch the hole location into the mount.

Using a Center Punch, mark the hole's center location on the mount. (This keeps the drill bit from roaming, and allows the hole to be drilled where you want it)

Drill a pilot hole. A pilot hole for the screw is created by using a drill size that is the same diameter(size) as the unthreaded shank of the mounting screw. You can begin by using a smaller drill bit like 1/16", then increase the size of the drill bit's until you reach the correct size needed for your pilot hole. In other words, the first time you drill, does not have to be the final pilot hole size, you can work up to it.

Clean out the holes of any drillings.

Lubricate the screws with light grease.

Assemble and tighten with confidence!

Take your time. The combination of drilling straight (90 degrees to the mount), plus, the correct size pilot hole...yields a satisfactory result, even though your apprehension about not much material to work with is absolutely correct IMO! Good Luck!