Had her since new and plan to keep er till she blows. My friend had a 67? truck with the same motor and made it 260k before he sold it, he also had a van with it that got beat hard for 185k til he scraped it cause of the 3 spd column

 

Dad's old '82 300-C6-4x4 got 10-12 mpg pretty much no matter what, not having overdrive didn't help much. Stock tire size. When it was a 2wd-4spd OD stick-2.47 rear axle, it did better, maybe 20 mpg on a good day.

My '94 300-E4OD-stock tire size-3.08 rear axle gets between 15-20 mpg. My Sable gets a lot better (20 with a lot of idling due to cold, up to 30), and has snow tires, so it is the go-to choice most of the time lately.