I recently came in possession of a pattern ship from the late 80's. Needless to say, the engine that was used is no longer available. I have been looking at engine dimensions and can find nothing that will fit the mount exactly, and I cannot change the mount since it is permanently installed. Currently, I have a four-stroke mounted in by the two front bolts (don't worry, I'm not flying it like that!). The mounting bracket on the engine does not quite fit the back two holes. I thought about drilling another set of rear holes, but they would have to be drilled so close to the existing holes that I would end up having one big hole that nothing fits in. Any solutions?

What was the original engine?

I agree with 8178 to try to find what the original engine was and then maybe find one of those engines on eBay, RCUniverse, etc. You'd be surprised at how many older engines are still available. Failing that, I have cleaned the existing holes, filled them with epoxy, then redrilled new hole locations adjacent to the old hole. Not the greatest solution, but simple. I used that method on a Taurus that had a Super Tigre 51 originally installed and I replaced it with an O.S. 46 FX. Also, I put a drop or two of Gorilla Glue in the hole when I screwed in the new screws(hex head machine thread type screws). It has flown well since.