See photo. What I did was used 1/4" bolts, that way they just bypassed the threading in the engine base.
1) 1/4" bolt.
2) Rubber grommet, which smashed down really flat once wrenched down. Then a metal washer, and finally a nylon washer making contact with the frame of the mini, so that they can act as sliders, protecting the paint when I need to loosen and slide the engine and make chain tension.
3) Underneath the frame, metal washer and nut.
This seems realllllly tight when I wrenched it all down, so I'll get it running again soon to see if vibration loosens anything. If it does, I'll grab some blue locktight and maybe that'll do it.