Thanks for the responses.
Yes, we will be in a hire car that we hired out of Portland OR and after LL we would be heading back west through Kamloops and Vancouver before crossing back into the USA and returning to Portland.
However, as Australians visiting this part of the world, we aren't sure which is the best way to go and what to see along the way.
We did look at a stop in Great Falls (because its about halfway, give or take a bit) and I am still doing research to work out the details.
The Battle of Little Big Horn site sounds interesting as does the Lewis and Clark Museum. Is the museum in Great Falls or Billings?
Any other suggestions would be most welcome. Thanks for your help
However, any tips or advice is appreciated.