head gasket guru's

[bp71k5]

While I was setting the timing on my motor, I discovered a coolant leak started while I was watching. It was leaking out from between the head and the block so I assumed I blew a head gasket.

When I removed the head, I didn't see what's I've normally seen from blown head gaskets. I don't see any burn marks to the block, head, or even the gasket. The only evidence I see of a problem is the bad combustion in the two rear cylinders. The area circled in green was the general area where the water was coming out and is right above the two cylinders which had lots of deposits in them.

On the gasket picture, the area circled in blue looks like the gasket had a some water pressure building up behind it because it's cracked right next to the hole and has a large bubble behind the crack. But the edges of the gasket look normal. I was told the engine only had 25k miles since the last rebuild.

So did I just catch the problem before it did any real damage or is something else going on. The spark plugs were replaced last week and the rear one or two were very clogged with gunk when I pulled the head last night. I don't know much about the internal workings of the cooling system, but I just want to make sure I fix any problem in the head that caused the gasket failure before installing new gaskets. Is it possible to have some gunk stuck up in one of the water passages which would cause this or does this just look like normal old gaskets.

 

[4X4HIGH]

Those look like 461 casting 327 heads. When water enters a cylinder it will clean away all carbon so i can tell you that you did not have water entering a cylinder. I would suggest having the head(s) magnafluxed for any cracks and pay particular attention to the area you've noted. I've seen heads crack on the outside area around the lower row of head bolts so that's where i would first start looking.

 

[bp71k5]

The head casting number is 3991492 which my book lists as a 69-70 sb350.
The engine number is 3959512 which lists as a 62-63 sb327

The pistons are also marked .030 so I assume that means the block was bored 030 over? I wouldn't be surprised if the heads were not original to the engine since the PO said it was rebuilt after he got it.

What I really want is a 350 and am on the fence on whether it's worth rebuilding this block with a bigger crank and other stuff to make it a 350 or to just get a used later model 350 with good compression and TBI to replace it.
Are the newer blocks better platforms for building or do you have any leads on a decent 350 longblock/shortblock/used motor? If I can find a good motor, I can just build this one back up and sell it for a few bucks after I get the 350 running.

 

[bp71k5]

New info, I went out there last night and happened to see the inside of my valvee cover and it had a lot of light tan sludge on the inside that looks exactly like water contaminated oil.

Was water somehow getting into the valve train area? This is weird. It looks like I need to drain the oil and see what's up.