Don't know about differences between right and left hand drive unfortunately.
I bought a heater core from these guys
http://scherbragroup.com.au/automoti...ers/index.html
Ordered it over the phone and had it delivered to the workshop that was installing it for me. Worked out less than half the cost of a genuine item.
When I ordered mine there was 2 different types but they've changed their site layout a bit now and in the pdf catalogue in only shows one listing for the WJ now
I've heard of people having the core repaired at a normal radiator shop so this may be an option if you can take it all apart yourself.
When they did mine, I'm pretty sure they dumped all the AC gas but not 100% sure if it's absolutely necessary or not.