Hi RoscoeFink,

Used to live in Mackay back in '78-'80.

I'm always trying to do the same, build a ride with whatever I can get for free or next to free, only buy retail what can't be had otherwise. Don't know much else you could use from the 1979 mercury marquis except the drive train. If its a decent car you might consider selling it and use the money for what else you could dig up.
I remember seeing lots of ranches out there with old cars sitting out in the fields. Maybe able to make some deals with the owners if there are still those relecs around.