It can be done, but the cost doesn't make it worth the bother. You can save fuel a lot easier by doing other mods that are easy to do, and reasonable in cost. If you want me to help you out, shoot me a private message.
The upgrade to the MDS would be expensive. You'd need a complete wiring harness, computers, and such out of a donor and then the lifters etc. Like Duane said there are a few things you can do that will help fuel mileage now.