For what it's worth....I am in-process on a Funtana. When I mounted the engine (Saito .72), I used the self-tapping socket-head screws that came with the model for mounting the engine. I've screwed them out and back in a few times while building and it still seems like a very sturdy mounting job.

Considering that your mounts came with screws and the difficulty you'd encounter going the bolt and nut option, I'd vote for just using the screws.

I'm sure others will weigh in on this.

Jim