gas mileage on an '89 5.0 AOD vert?

I'm possibly going to be buying an '89 5.0 AOD convertible with 80,000 orig. miles. I was just wondering what kind of mileage i should expect. My '84 gets 16 or 17 usually and it's a pile, so i'm hoping this newer car would be better. Most of my driving is city driving but i do take extended trips sometimes. Thanks in advance!

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'84 Mustang 5.0 T5, FMS aluminum radiator & 180* t-stat, 1 5/8 shortys/2.5" duals, '88 GT tail lights and wheels, Holley 4160 4 BBL, FMS smog pump idler