Need help with diagnostic / cracked head or block?

New to the forum. Came here because I’m having trouble with my 2000 Tahoe 5.7 need some diagnostic advice.It’s has 137k and is very clean. It got a lot of oil changes. I discovered coolant in #2 and #4. I replaced both head gaskets. Fired it up engine still smokes a LOT. Not oil..it’s white smoke so it’s still sucking in coolant. I did a compression check and #4 was only at 70 lbs. I did a leak down test… sort of. I put compressed air in #4 at TDC compression stroke and could NOT hear air leaking in the intake or exhaust however I DO hear it if I stick my ear by the oil filler tube aka air is leaking into the block. I would first simply think it’s bad rings or stuck rings but that would not account for the coolant getting into the cylinder right?? So Now I’m trying to decide is it a cracked head or a cracked block or piston rings or what?? I’m hoping it’s just a cracked head but I don't know how to figure that out. Of course I could take it all apart again but I might end up just buying a long block. But… if it was in fact just the head that would obviously be WAY cheaper and easier to deal with. Anybody have thoughts on how to decide if I have a cracked head or block and how to tell which?

I did not see any visible signs of a cracked head or block when I had it apart but I must have overlooked it. Problem is I don't know how to tell which it is. It's not the head gasket now as I replaced that. It would be fantastic if it was just he head! Guess the only way to figure it out is take it all apart again and look much closer. But the fact it leaks down pressure into the crankcase must mean bad rings right? I mean is there any scenario that a cracked head or block leaks the compressed air into the crankcase?

Unfortunately looks like I'll be buying a new motor :[ Thanks for that link... lots of good info in there.