Thanks for the post! Helps me out a lot. Seems like it's going to be difficult.

The thing is: I live in Germany and the amount of good cylinder heads I can muck around with is limited

My engine is currently running on LPG (that's a butane/propane mixture very common here in Germany, as prices on regular gas are about $8 per gallon )
LPG costs half as much, has a higher octane rating and burns more efficiently, but it also has a much higher burning temperature (and higher octane = more compression possible = more efficiency = even hotter). So in regular heads I might get cooling issues (haven't so far, but I've only put 5k mls on my gas system). So with my new cylinder heads (got another set of 492s) I've polished the combustion chambers and exhaust outlets (less surface area = less heat dissipation into the coolant passages) and the underside of the valves. The heads are getting hardend exhaust valve seats, too.

So the next issue would be to reverse the coolant flow, but on the other hand that would be a load of work. I've thought about water injection as well, but that's not street legal here in Germany, and this is going to be a daily driver.

So I just thought maybe there's an easy way to do it, but I guess the Gm engine engineers new what they were doing building it that way... And if they bust 100 engines in a series of tests till they get it right they wouldn't care, but I (and my wife ) would care...

I'll have to think about it. I'll let you know if I try to do it And I'll never tell anybody it I fail