Late MX5 engine more complex to fit??

[PorkChop]

How complex do you want to go with the electronics?

The mark 3 engine (MZR) and box is very different to the mark 1/2/2.5, it's the same basic engine as the Ford Duratec. The bellhousing pattern is different to the earlier BP/B6 engines. In fact, there's not much carryover from the mark 1/2/2.5 to the mark 3, full stop. The mark 3 stuff is also much more expensive. The cheapest MZR engine I could find on sale was still over £1k, and a 5 speed box was nearly £200. I would be extremely suprised if you can find a mark 3 engine for £150 (or a mark 2/2.5 engine unless there was something wrong with it or the seller was desperate to sell), whereas you'll have the pick of mark 1 engines for that.

If you had a mark 2.5 engine and want to keep the VVT, then that dictates what ECU you run (read that as not being the cheap end of the scale).