I have a plane in which I am not happy with the positioning of the engine mount. I want to remount it.

What do I do about the holes from the old mounts? I was thinking of using some dowel rod to plug the holes. Any other ideas?

well what sort of model is it, need a little more info, and what sort of engine.

depending on the size of the holes, you can either make dowel rod plugs or just epoxy them shut with some five minute epoxy. I've used both methods.

I drill the holes out to the size dowel I have on hand and glue it in flush with the back side of the firewall, then sand it flush with a dremel on the engine side. This way extra dowel will not interfere with new blind nuts.

Thanks for the answers, I kind of figured the Dowel method was best.

FWIW, it's a Goldberg Ultimate, it was originally a kit plane but I bought it at an estate sale and am in the process of getting it ready for the type flying I plan on duing with it.
The plane had a Fox 74 in it but I prefer a four stroke so I am putting a Satio 100 in it. It won't be a super duper 3Der but it should end up being a fun flyer.