My '56 weighs in at just under 10K with just me in it, tooling along at 55-60 it got a little over 9MPG on a fairly flat route. Add a load and some hills, it's hard to say what to expect. Best bet is to do some testing.
1956 GMC 370 dump " 'Tater "1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI
I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P