I like the concept, Jeffrey Milne! I think you're almost there with the logline.

Here's a logline suggestion (I put everything in one sentence): "After twelve long years, a Mail Coach driver sets out to avenge his father's murder and retrieve a stolen heirloom from the bushranger responsible, putting his life and future at risk."

You can remove "family" because you put "heirloom."

Thanks for the feedback guys.