If they are made in China, and sport a 506 casting #, they are counterfeit. Good or bad, that's what they are. A true 506 would have been cast at the GM foundry. If they are not counterfeit, they are the same old blocks, recycled. I don't know which is better/worse, but time will tell. Most folks just want a good product at a good price, as with most things.

I agree about the GEP blocks. But, the lack of availability is likely due to military obligations, and limited production ability. Let's face it. The 6.5 is seen by most as a dying breed and not a sound investment. The few of us left are but a small niche market. In most cases, competition is good, but I doubt Navistar will change their production practice. I can't say I would do it any different. They are what they are, and are available, at a price. You can get them, just not at a price most will tolerate. So, here we are. Doing what we do, in this love/hate relationship.