Thanks everyone for the responses!
One thing I love about the mira is how much it revs. So I have always gone away from the idea of an EJ bottom end. I have read they are not well balanced from factory and don’t like much more than 6000rpm? An EJ block with my EF head is definitely a possibility though. I have thought about it a lot. I would want a turbo upgrade if I did that.
I have toyed with the idea of fitting an EJ head to my block. I like the design of the EJ cylinder head - it would rev and flow better than my EF head, which would be nice when I want to turn up the boost. I’m yet to play with wrecker motors to see how well/if it would work. I know there is the obvious oil drain in the EJ head that my EF block doesn’t have, but I could sort this by having it welded up, then drill and tap and do a head drain similar to what people do on Nissan RB engines.
I would need to modify an EJ loom to suit, make new manifolds, and a stand-alone ecu would be pretty necessary at that time too 
Lots to think about…