A couple of points. First, I never use either sheet or wood screws on any engine bigger than .15 displacement. I have had them break. If you do use a screw, use a sheet metal screw because they are straight and have deeper threads than a wood screw which is tapered. Sheet metal screws are just not as strong as machine bolts. Second a 1/32 inch space between the side of the hole and the edge of the beam on the engine side will not be a problem. I have had that much space on a number of installations and never had a problem with the mount breaking.

I mount my engines to both plastic and metal mounts by using the largest allen head bolt that will fit the engines mounting holes and then drill and tap the engine mount for those bolts. I use a lock washer between the head of the bolt and the engines mounting holes. I have never in 40 years of doing this had an engine come loose or a mount break (except in a nose first crash). On some mounts I have used a bolt with lock nut but because of the taper of many mounts, this is not aways pratical.

Bruce