I've run a Minor with only 3.5" clearance under the engine bashplate and it was useable. The only time I grounded it was when driving onto a pavement area that started with a V. I drove onto the V, forgetting to put a wheel on the kerb and had contact.Hey all, random update, the engine is in and the box also. The engine sits in very low as the clearance issues with the steering rack. So now it looks like the sump will be only about 6 and a half inches from the road surface. So I was thinking about a rather radical idea.
If you can put a bashplate at the front to allow for parking incidents I can't see that 6.5" will be a problem.
For serious offroad use I raised the front to 6.5" and it took some mean bumps and ditches to hit the ground - certainly couldn't have grounded it on European roads!
This was with standard minor torsion bars (51 years old) so if you have new uprated ones, it will add an extra large margin.