Actually, the most popular swap in the Miata is the small block Ford. They fit really well and there are several companies that make kits. I've seen one. It was anything but boring and slow. lol
Well considering that ford owned Mazda for a while that don't surprise me....
Just because I'm so tired of the old "stick a Chevy motor in anything" if I wasn't gonna run a Mopar, I'd run a small block Ford too.