So, here is where I am with this.
Front cover and gasket- I agree. Easy choice as potential culprit, but hard to change and would like to rule out other things first.
Intake- At what point does the coolant go negative pressure?- decrease in pressure I can see, but negative with respect to crankcase or atmosphere? I know I wont let go of this, but I still am missing something that gives me a plausible explanation for how lower intake gasket can cause oil in coolant..
Head gasket (HG)-I know I have oil in coolant- seems that the guys with the chemical method for testing for hydrocarbons in coolant would say that's all they need to know to determine head gasket failure. You said in your last comment that your experience is that a HG fail will cause overheating. I have seen this as well. Perhaps, I am just seeing the early stage of the HG fail (i.e. some "blow-by" of exhaust into coolant, but not to the point where it is causing massive gas pockets and any over pressurization of coolant system is just being bled of by cap)
After reading around a bit, I believe I want to pressurize each cylinder at TDC and look for bubbles or rise in coolant level.