Sportsmans came standard with the chrome mirrors, colour coded vinyl roof and Volante alloys, so if your spare is a Volante, I'd say your car is a Sportsman.
Also the only picture I have of one has the bonnet ornament and C pillar badges, so I'm guessing they all had them.
There could have been a few other differences but thats all I know of.
Then JH means your car was built in Australia (J). The H means it was built at the Brissy plant (G is for broadmeadows)
and the 37 tells you its a Fairlane 500, (Marquis were stamped 63)
Have a read of this page - http://www.fomoco.com.au/ID.html
Be aware that most of that page refers to XR-XB Falcons, though you get a fair idea of what it all means
I dont have '78 paint/trim codes on me but basically the only exterior white of the time was 'Sno White'.
Trim colours were Black,Cream,Saddle,Dusk and Jade. The first two are self explanitory with the Saddle being darker than the Cream, more like a tan colour I spose. There was a bluey/grey colour that I'm guessing is Jade, and I wouldnt have a clue what the Dusk looks like
Anyway, I'll stop rambling on for now