Don't worry about the complex stuff like cracked cylinder heads until you've checked out the simple stuff first...
Are you SURE that the oil level is OK? You say the light flickers on under hard acceleration, that might be because the oil level is marginal and the pressure might be dropping if the oil surges away from the pump pickup...just a thought.
Could also mean that you need an oil change, when was the oil last changed? Oil does break down under the pressure, heat of the engine and becomes thinner with age so the lack of pressure could be down to oil that's past it's best.
If anything is broken t's far more likely to be the oil pressure switch (which will only cost about £30 to swap over) than a cracked cylinder head.
Mind you, I wouldn't want to be doing an indicated 170 with any doubts at all about the oil pressure...not without one hand on the clutch anyway.