RE: Pulse XT 40 Engine Mount
Use a different engine mount.
Some engine mounts come in two pieces with oblong holes.
You can adjust the width of the mount while the actual mount hole locations remain constant.
See this: [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJ772&P=ML]Click me![/link]
If that does not work you can do what we normally do.
Get a standard width hardwood dowel from a hobby store... say a 1/4" diameter or less dowel.
Cut 4 small pieces off squarely.
Tap out the existing Blind (T) nuts.
Epoxy the small pieces in so they end up FLUSH with the BACK side of the firewall ( you want the flush on the back as you'll not be able to get to that later! ).
Use a Japanese razor saw or sanding wheel to cut and sand the front side flush...
Mount the engine on a mount PROPERLY.
Put the mount on the firewall and center it perfectly and mark the location for a new set of holes.
Drill the holes and install the T nuts again.
Now mount the engine.
Except for the epoxy drying it almost takes me as long to write this as to do it!