Super Six fuel mileage

The OP requested mpg values for a bone stock slant. Did that mean bone stock everything? If so, then you would be hard pressed to find one from the 1960s when Chrysler was touting 30 mpg from the economy Darts in contrast to the performance Darts.

The poster on the slantsix site did a few inexpensive modifications that anyone can do and achieve mpg comparable to modern cars. That was his point.

30 mpg out of a slant six is very good. My 1995 3 Liter v-6 Toyota Camry gets 30 mpg on the highway. It has an overdrive automatic tranny, 15 inch tires, and a economy setting for the fuel injection in order to get it. The advantage that this engine has over the slant is that I can turn off the overdrive and hit the "power" button and get really good power out of it.

Oh yeah, the car has 176K miles and still gets 30 mpg.