Had similar hassles with my 82 Gemini years ago.
When I was in NSW I built up a worked 2litre Jackaroo motor with weber, ported early 1600 head, mild cam extractors etc. I didn't change the engine number, and the 1600 and 2000 blocks are pretty much identical externally. So it passed the yearly pink slip without a problem.
When I moved to VIC I had to get a roadworthy before I could register the car. If failed on lack of pollution gear. So I fitted the standard 2000 head with air pump, EGR, standard carb etc. Mind you, every hose was blocked with a ball bearing and the air pump did not have any vanes in it!
It passed.
But then I had hassles with VicRoads who said it was not legal with the 2000cc engine and demanded and engineers certificate. Finally I managed to convince them that it was legal as the 2000 was an option in Japan and it bolted straight in. They checked on the computer and found they already had nine Geminis registered with a 2000cc engine. So I finally got it registered.
Not long after I sold the car. I sold the head, cam and carby in the Trading Post. That old Gemini is still running around Geelong with blocked off pollution gear!
The laws have since changed - if you already owned the car interstate, you don't need a roadworthy when you register it in VIC. And of course there is no annual roadworthy either.
