3" wheel spacers would wreak havoc on your wheel bearings and alignment. You can seriously NOT do this. Proper wheel backspacing is the way to go, and try not to go with the biggest tire you can find.
No matter the motor, you will want to regear. You may get better highway mpg for a while, but your transmission will go if you rag on it frequently. Some transmissions, like the A4LD, are not heavy duty enough to deal with a daily beating.
Look around for tire fitment threads. I would suggest going with 33x12.50x15 tire, 4" lift, and cut your fenders. It will be just as functional, and your D28 joints and hubs will not crap out on you.