Spring on engine mount.

[Tony Griffiths]

Use the later rubber mounts except the one that's through the middle of the c/case and yes nylocs or double nuts at the back.
At the front slightly longer bolts trimmed to a length that pinches the rubber washers when they bottom out on the blind threaded holes in the forged nose of the chassis.
I had a crankcase a couple of years ago to convert. On looking at it closely both front mountings had been sheared out of the case and gas welded back together.I would suspect it was serious  accident damage rather than chassis flex though.

Thanks; of course, the front mounts are blind holes. I'd forgotten that!