The key is don't tip your hand by asking for an 848 head. Ask for 56 and later head, and don't start drooling all over yourself when you find one. Chances are most people know what an 848 is.
Just say you are looking for a 56-63 235 head.
The 848 heads were the most common high-pressure 235 heads - roughly 75% of the heads.
I think the drooling over an 848 head is drooling over one that has no cracks and has been certified/tested/guaranteed for no cracks, as Deve pointed out.
