Mick
If you want to change the engine/gearbox in your 4/4 then you have plenty of options that have been tried and tested. I think the Mazda route is relatively unknown , so you would be in pioneering mode . Great if you have the skills, patience and perseverance, but they are becoming rarer.
The 2 most common routes seem to be:
A Ford Zetec engine 1.8 or 2.0 (plenty of availability, cheap-ish parts, lots of tuning possibilities)
A Vauxhall VVTI 1.8 (several have followed this route, but the originator has now stopped this kind of work for other avenues) Very effective, not quite as easily available) Tim (Hamwich on here) has this conversion. I'll let him give you the story from the horse's mouth.
The crossflow engined 4/4 is no slouch, and may well prove to be enough, the T9 box conversion is a really worthwhile mod as cruising with the 4-speed box is quite tiring at the higher rpm.
Good luck
