That's awesome, what part of Australia are you coming to. It would be good to meet up. Cars are really expensive here though, we have insane taxes. If your car is built and custom I think bringing it would be a good idea since it will cost you alot to buy another and build it. Just make sure you have found out every single cost since customs and transport here desperately want to squeeze more money out of you. Make sure the car is spotless, literally not a grain of dirt since quarantine will make sure to check every part. Not sure about the cost of LHD to RHD but maybe sell your LHD dash and everything you don't need and buy them here as RHD. It's gonna be a bit of a hassle but your car looks clean and you sound like you have done some great work to it so by all means welcome. I'm in Sydney by the way.
Going back to topic I wouldn't mind spending 5-10k honestly if I can get a good solid 370hp. My other worry is the gearbox, I suspect it would need to be reinforced. Not sure about a shop that would do the sleeving and rebuild. I'll look around.
As for 2JZ or LSx I just don't wanna go that route, I'm no fanboy but I want to keep this a BMW in every way including the engine. A 2JZ would just ruin the car especially for a DD like I want it. I know the 2JZ is an amazing engine but let's be honest, unless you wanna make 1000hp it's not worth it. As for the LSx, it will gain much more HP but it's not gonna be cheap. I'm not gonna fit some old LS1, LS2 or LS3 in the car then have to worry about the electronics and what not.