A few old build pics:

Just a single front coolant hose fittling on each tank now.

 

Motor is out.

 

 

Saw something Frankenstein like that in Ford world and had same issues....it was the manifold design cause distribution issues

 

Pulled the bank 1 head last night. Here's a few pics and a link to the rest.
























Album Link

 

i spy an issue.....why is your coolant passages blocked

 

Looks like they are only using the small holes. Not sure how good that is for the street. Seems they think it is good enough for a race motor.:
Top Ten LSX Race Engine Build Tips From Late Model Engines - EngineLabs

 

all 4 corners need to be vented for a boosted applicaiton, if you have doubt put a coolant sensor in the rear ports of the heads...youll see 25-30* warmer temps

so if you have a 190* stat and now your rear cylinders are seeing 220 before a run, what do you think they get after a pull? motor temps raise up so rear cylinders will increase and alot of time pistons and the cylinder walls dont agree...this is typically why you see the rear cylinder distorted and ppl claim it popped the piston on 7 or 8

have doubt look into kurt urban

 

Coolant passages or steam ports?

From what I recall the left rear steam port sits under the back edge of the intake.

 

It can't hurt to vent the rear ports but it's certainly not the sole cause for your failure. Some of those exhaust ports look like crap. If I was you, I'd throw in a good known JY motor and let it eat. That way you take any motor issues out of the loop.