The motor package from a Leaf is about 90kg so probably in the same ballpark as the fuel tank, rear axle, and gearbox. You'd then need to get a lighter battery because a Leaf's battery is about 350kg, or twice the weight of an MX5's engine.
There would be a lot of surgery involved on the back end but since it's a subframe with the diff in the middle you're halfway there.
And for once, the project car's totally rotten boot floor won't be a problem because you're cutting all that away anyway!
Meanwhile, Ford has been selling the Mach-E motor as a crate motor for years; but it's useless, because they sell nothing else for it. No battery pack, no controller, no regenerative brakes. Pretty much a PR sham. Why bother?
I have a Mustang with a half-disassembled engine that needs major work, so I thought hey this might be cool. Nope.