My last 87 4x4 318 auto would do 17 mpg highway all day long and 14 city. My 84 2wd 318 would do 20 hwy and 15 city. So you are easily 4 to 6 from what it will get. 50 bucks in parts and a good 4 to 6 hours could get you where you would like to be. What other mod can you do for so cheap??? One tank of fuel the savings would pay for the parts. I am done with this post.