Hi Nickel isn't needed for racing. That's all hype. I think the whole nickel content theory is hype. Sure it's nice to have so go with the oldest block you can find. The older the better cuz things were made better and stronger back then. You get an 80's 3970010, you just have run of the mill block. You get a 69-70 block you probably have one high in nickel. Racers shouldn't even give a rats ass. They'll be rebuilding it soon enough anyway if they're real racers. I rebuilt my engines about every 2-3 years. All a high nickel block will do for you is your bore will last longer and the rings don't wear the bore as fast. That's it. So in reality, the guy building an engine for his Square that he wants to last 15 to 20 years, he's the guy that should care if he has high nickel or not. I do not care. What's more important to me is that the line bore is perfect so I don't have a big expense having the block line bored and cutting my main caps and my head surfaces are flat and not warped.