When the engine mount is installed, it's clear that the firewall corners are in the way for a fit of the gear legs in the engine mount. You have to grind away a fair portion of the bottom outer corners so that the landing gear legs will slide in the engine mount leg holders. Make sure you con't go too far. You don't want to grind into the vertical part of the firewall.
Here is what it looks like on the passenger side.
And the pilot side
I temporarily mounted the engine mount on that from the bottom, it looks like this on the pilot side.
And the passenger side
