I am thinking about buying a 88 Ranger 4X4 with the 2.9 liter V6. It only has 56,000 miles on it but I know the 2.9s don't have a great reputation. If I buy this thing, how hard would it be to eventually put a 4.0 in it? Thanks

 

Unless you're wanting the 4.0 for gas mileage, go with a 5.0. Bout the same labor as it would take for the 4.0 but with much better results and performance options. Whichever way you go it would be best to get one from a donor vehicle so you would have most of the parts you'd need.