I found on the black fiber engine mounts if you use the correct tap size drill, drill it out then use a SOCKET HEAD HEX SCREW driven with a drill you can
drill the screw into the mount. Grind a small taper on the bolt screw before you start. Then be quick running it in and quickly reverse to run it completely out. There will be heat generated and the thread will be hot enough to mold around the screw. Do this several times until you are satisfied that you can hand screw the screw into the mount. I have never had one come loose as the mount acts like a locltite device. If you are concern of comming lose you can through drill before you power drive the screw. Then you can also put a nut on the back side.

Given you are working a 1.5 you might want the nut. DON'T use 4x40,, 6x32 minimum.