The hard part of doing a long-arm suspension is not building the arms themselves. That's exceedingly easy. It's building the control arm mounts strong enough, high-clearance enough, and without interfering with anything else. Once you do that you can slap a set of arms together quick. It would be silly to go to all the work of building a long-arm setup for only 2" longer arms.
You *could* use the longer arms with the stock mounts, but it would relocate your axle, which may cause tire/fender/bumper interferance, could require a new drive shaft, brake lines, upper spring and shock mounts, etc. Again, it would be a ton of work for negligable gain.