A big part of mpg is related to total gear ratio. For that you need to know ring gear/pinion ratio, top gear ratio and last but just as important, tire diameter.
Example
IF, you're running a 3.73 rear end and 26" tall tires with a non-overdrive transmission and going 70 mph your 327 is turning 3,374 rpm. If that were the case, 10mpg sounds about right.
Add a .72 overdrive to the above scenario and you're looking at 2424 rpm when running 70mph. Not only would things quiet down, you'd likely see a major mpg improvement.
This might help.Good Luck,
RonR
