I'm sure it was only the top/inside edges of the mount that needed a little "bevel" to allow the engine to seat, with the engine lugs squarely/flatly on the surface. What some people don't think about is, the engine's lower case is ROUND.. thereby there should be plenty of "meat" left to drill/tap the holes...
If its a plastic mount, do yourself a favor, and be sure to use machine screws(allen-head preferably).. 4/40 for .40 size and smaller, 6/32 for .60 and larger is a rule of thumb.. the plastic mounts tap very nicely, and you can use a nut on the backside if you want.. other then that..a lock-washer works very well too. In my experience, the self-tapping, sheet-metal variety screws don't go well with plastic mounts.. they tend to stretch the plastic.. and the mounts usually fail on the inside hole(closest to firewall), as thats the weakest point once they're drilled.. just an FYI there.. Good luck.
