No, I have not done this but its come up a few times in recent threads. I know nothing about this really but saw a 1.6L MX5 on ebay for $100, running well it said. So i thought i would post a couple of pictures....
Apprently early 1.6 engines had some sort of issue with the front of the crank which has to be welded and machined. Something to be aware of I guess. I would amagine the later 1.8 would be a nice one to use.

Anyway, it appears from the pictures that the sump would fit ok in a bellett. Starter on RH side though like Gemini engine. Front mounts look possible also.

Have seen complete engines and boxes, even half cuts on ebay, up to $2000.

Gearbox an issue as the shifter is mounted way back on the box. As somebody commented here, about in the back seat of a Bellett.

You could mill off the Mazda text and engrave ISUZU instead, and maybe fool your dog.

Keep the bonnet shut at any Club meetings though LOL

glenn