Definitely check with your insurance company. People go around saying that because its the same engine that the insurance co won't care. I don't think this is correct. If you changed engines for a more powerful model and didn't tell them then you have just handed them a great reason not to pay out on your claim - in which case - why have insurance at all.
As for engineer's certificate - I know nothing about the Tas regulations. If you did it up here in NSW then you probably would but I'd guess that it would pass no worries even with standard brakes.