The 2wd head has less meat in the waterways so more prone to corrosion, the upside is it has the mounting for the turbo damper unlike the 4x4

Also the early 3drs have smaller holes for the head bolts.

Like anything that evolves then the newest version is the best as its had the bugs ironed out.

I believe the latest brand new castings are a hybrid of 2wd and 4x4