ORIGINAL: bkdavy
Depends on the type engine mount you're using. For the typical glass filled nylon engine mounts in use today, I like to get the engine set where I want it and use small C-Clamps to hold it in place, I then use a spare pushrod, heat it up with a soldering torch, and then use the rod to melt into the nylon to mark where the bolts go through. Take the engine off, drill the holes, and then bolt it on.
Brad
I like to place two dots of CA glue on the mount, find my drill centers with a Great Planes dead center locator, break the engine loose from the mount and drill my holes. Works on aluminum or plastic fiber filled mounts.
Bill