Ok, what I started with was a biscuit motor mount that has the two offset bolts as shown in picture. I cut off one threaded bolt flush with the plate. Doesn't matter which one. Then I drilled out the remainder of the bolt all the way through the mount. Now there is a hole all the way through the mount.
Then I inserted a carriage bolt all the way through the mount so it sticks out just like the one I cut off. Only now it holds the two steel plates together. The motor mount can’t come apart when installed, as one of the bolts goes all the way through it.
A common complaint on the biscuit mounts if that they separate when too much torque is applied. This solves that problem for free. Only need it on the drivers side.