We had a 4 door version (GL-10) that provided us with high 30's as an average, not all highway, but an average over it's lifetime. However, ours was an '85 manual with single range final drive, only part-time 4wd (because of no center diff), and no limited slip rear diff.
You might wish to put the spare tire carrier back in the car as it functions as a strut tower brace. I think it can be used even with that intercooler that has been added.
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