One very important thing is that nearly all the parts are still on offer in Australia. Aussies are friendly and willing to help.
I'd sugest you go over Jack Collins (Mustang Six's) Crossflow Chronicals in the tech section. Please consider getting the engine rebuilt in Australia before it arrives in the States.
If you don't, you'll have many long nights here going over the items which you need to source locally. It only needs one substandard part to mess up a great engine. Having siad that, the choice is yours, and Jack Collins rebuilt his. I believe his son is enjoying it now in his white Mustang!
The x-flow has a significant amount of US spec 351 Cleveland and 351M/400 bits in the valve gear that can be cut down to fit. Lifters, sled fulcrums, head bolts are the same. Valve springs can interchange with some carefull research. The oil pumps, pushrods, water pumps, and hex drive and distributor have differences which require a bit of work to allow the US parts supply bits to fit up. You have to duplicate the stock Aussie bits if you want a lot of domestic bits.
The main bearings differ in crush and thrust widths, and the timing chain has an extra link in eaxh direction, with the same aftermarket crank gear and cam set that FSSP sells. The 250 rods are same as the US ones, and rod bearings are the same but have a specified crush which differs to the Aussie xflow. Pistons are similar, but not the same.
The best thing is to go over the engine part numbers Ford lists, and check if you have enough budget.
All bits need to be rebuilt unless you have a pristine orignial part. Here's a Ford Basic Part Number list I use to jog my memory. Ford itemises every item in it cars, and keeps a standard part which is either avaliable as new old stock, or reconditioned, or brand new from suppliers.
6015 I6 block
6019 front cover
6020 front cover gasket
6024 front oil passage plug
6038a rhs engine mount
6038b lhs engine mount
6049 head
6051 head gasket
6057 valve seats
6110 piston
6135 piston pin
6149 ring set oil, comp
6200 connecting rods
6212 rod bolts
6250 camshaft
6254 oil pump gear
6256 cam gear
6303 Crank
6306 gear (crank)
6316 valve train damper
6375 flywheel
6384 ring gear
6500 lifters
6521 intake gasket
6563 rocker shaft
6582 valve covers
6659 oil pump
6700 oil pan front packing
6730 oil pan drain plug
6750 Dip stick
6754 oil level indicator tube
6766 breather cap
6775 oil pan
6837 fuel filter
7003 manual gearbox to suit T5, single rail, or Aussie C4 bellhouing
7600 pilot bearing (if manual, its same as US)
8150 starter
8503 housing
8507 water pump gasket
8509 pully
8511 shaft
8512 impellor
8574 thermostat
8574 seal snap ring
8577 fan belt
8600 fan
8620 alterantor belt
9202 float assembly
9350 fuel pump
9425 i6 intake
9430 Ex manifold
9486 intake spacer
9510 carb
Once those are checked, you'll have to assign a cost to each, and multiply it by how many items.