To the best of my knowledge the only vehicle manufactured in any significant quantity in New Zealand, as distinct from being assembled from CKD, was the Trekka.
Welcome to the wonderful world of BMC ownership.
Serial and multiple BMC owner since 1983 here. You are definitely making the right decision to reengine your Mini. My first car was a Mk2 Mini 850 with the magic wand gear change. I had a lot of fun with it but nowhere near as much fun as the 1098 powered Clubman that replaced it two years later.