I have the IO-360 M1B as supplied by Vans with the matching firewall forward kit and I am currently bolting up the engine to the mount. On the bottom 2 isolators and mounting lugs they are not sitting flat as the oil sump casting sticks out past the flat engine mounting face as you can see in the photo attached.
In my firewall forward kit I received the 4x isolator kits which each included a large flat washer which is under the head of all 4 bolts and mounts, and then separately with the engine mounting bolts in the Vans kit there were 2 slightly smaller diameter large washers included, as you can see in the second photo.
My thoughts are that I could use these 2 washers on the front side of the BOTTOM isolators to space the engine mounting lugs out and clear the sump casting .. but I am conscious I could be adding up-thrust by doing so.
What are you guys doing with this?