If you do this, you will either need an adjustable trac bar, or those spacers that you can mount between the frame and the trac bar bracket, otherwise your steering wheel will be pointin in funny directions and your axle will no longer be centered under the truck.
My buddy had them on his 05 for a while, everything held up fine. He just machined some for my truck, and I plan on running them.
Also, usually with a 250, you need the 350 rear blocks to really be level.