Hi Nathan,
I bet that was a scary moment...
When we bolted our diff in we decided to use the diff washers mounted to a bracket welded to the underside of the diff plate.
The problem is my diff washers are badly corroded and I am looking to buy some second hand ones as I can't source new ones (unless somebody knows where).
The question I now ask is are these the only areas to look at? On the MX5 they have a substantial frame bolting the diff to the gearbox, I personally am now looking at my diffs rubber mount as well and will probably beef this up. Also I am going to insert a pressed plate between the two diff mounts taking out any twist between the two mounting points.
Probably overkill I know but looking at your photo makes me shudder...
You said you had no other damage to your chassis so was the diff rubber mount ok?
You also mention a spreader plate but not sure what you mean by this, so any photos or diagrams would help.
Sorry to hear about the setback ...Johno