New engine suggestion for 1984 Holden Gemini?

I am about to buy a 1084 holden gemini , it is a 3 speed auto and i was wanting to up the gears to a 4 or 5 and put in a new engine . I was wondering if anyone knew about how much that would cost and if you could give me any good suggestions of where i could get this done . I live in Australia NSW Sydney . Thanks alot :D