Coolant Recommendations?

I have been trying to figure out what type of antifreeze should be or can be used in my '66 225 slant six. There seems to be some concern that the modern organic acid inhibitor formulations are not compatible with the cooling systems of old cars, despite the manufacturers' claims that they are suitable for "any make, any model, any year." What about the so-called hybrid inhibitors (organic + inorganic)? Or is it best to just use the conventional (old) inorganic inhibitor coolants, assuming you can still get these?

I would be replacing the coolant every couple of years in any case, so extended life is not really a priority. I just don't want to use something that'll cause problems with seals, etc.

Steve