Not the clearest photos, but here's how I did the rear gearbox mount on mine - some 3mm x 50mm flatbar bolted tight on the tail of the box, mounted onto a couple of exhaust bobbins to take the vibration mounted onto a bracket on the chassis. simple as could be.
https://www.flickr.com/photos/446457...7632087827009/
https://www.flickr.com/photos/446457...7632087827009/