Hi Nigel! Welcome to the site. Lots of good people here.
Looking at a R-code Cuda eh? Whew! You must be well healed in order to be shopping for one of those! Being relatively new to Mopars, and with that kind of money to be thrown down to get a true R-code, I would seriously look at finding a broker, agent, knowledgeable authority, ect., ect., there in Oz to go look at the car with you.
I was lucky enough to have owned a true HemiCuda from 83 to 86. Back then I didn't know much about "numbers matching" other than the VIN having a "R" in the fith place and there being a Hemi under the hood. I had no idea if the block was the one the car was born with or not. There were probably a lot of things that were not "correct" on that car. I didn't care, it was a HemiCuda and it was mine. When I bought it in 83 I paid $11,500 for it. If I was able to aford shopping for a true R-code today I would probably be a nervous wreck considering that they are going for 15-20 times what I paid for mine!
Once again, welcome and good luck in your pursuit of the ultimate E-body!