What do the spark plugs look like?
Does the exhaust smell like fuel? Or bring tears to your eyes?
What's the stock PV supposed to be?

Most similar experiences I can relate:
My 438" Street Hemi RR, pretty big old-school low-vacuum Crower cam, 4.10s & 4-speed could burn through gas like crazy before we tweaked the carbs.
Like a full tank in 100 miles, with a few bursts of acceleration.
It'd wet the plugs and burn your eyeballs standing near its tailpipes.
36* total + vac advance, original AFBs, headers, 10.8:1, MSD6.
Leaned it some with staggered jetting, leaner metering rods & stiffer springs for the rods.
Got significantly better mileage - guesstimate 6-7MPG, including a few "exercises" every time I drove it - and the plugs & aroma cleared up.
Had a cammy 446" RB in a '64 Savoy, 727, 3000 stall & 4.10s, also thirsty, never accurately checked MPG but seemed about 6-7 as well.
Never tried to maximize MPG on either, mostly town & "hey, the road's empty" - so I'd bet on better #s at sustained cruise @ light throttle.