You would need an XR2 ECU, engine harness, knock box, distributor, injectors, VAF. The N/A parts won't work.
The chipped XR2 ECU will support ~250whp, after than you'll probably want a standalone ECU. SAFC's don't work on the B6 engine management.
To convert the trans, you'll need the XR2 trans, XR2 flywheel, XR2 clutch, XR2 intermediate shaft, XR2 axles.
The Miata heads are no better, they're the same. Can you point to the article in question? On the 1.8L, which is a different engine, the later Miata eventually got the BP4W head which is better than the BP05 head, but neither of these fit on the 1.6
Which Mazdaspeed engine were you looking at going with?