m20 overheating + oil in intake

[bitkill]

Hi!
This christmas decided to put bigger injectors on my m20b20! went for m50b25 injectors and put them in my engine :) Tuned AFM accordingly.
m50 injectors pic: http://imgur.com/shkMvbV
In my "test drive" with the new injectors the car runned great, very smooth, until it decided to overheat... a lot!
Had to put cold water to cool it down but it came out right away in form of vapor!
Had to tow it home and there verified that the thermostat was not working.
For testing purposes, I cut the thermostat and after 8-10 min the car was overheating again!
A local mechanic said it was the head gasket. Had to spend all my money in the gaskets + bolts.
So I pulled apart the engine head, lots of deposits, but the gasket seemed fine. some minor time-related marks, but no evident damage!
Also, when pulling apart almost everything, had engine oil until the AFM!
some pics:
link to imgur album: http://imgur.com/a/DXHxk#3 (for better viewing)

I am sending head to shop for smoothening the surface & cleaning valves.
I am afraid of putting all back together and doing the same thing! Any suggestions?

[jeffnhiscars]

You should never put cold water in to a hot engine or you risk cracking something. Overheating can also cause your head to warp.

How did you check the thermostat and if you removed it and it still over heated you could have a bad water pump, plugged radiatorn or internal coolant leak (possibly caused or made worse by overheating).