I think you have good long term instincts. I have always had the impression that what Gore Vidal is a humanitarian social democrat. That is he favors capitalism, albeit a demilitarized, constrained capitalism. He would like to see a very small military, and very little U.S. involvement abroad, strong social democratic policies -- including single payer health, child care, nationally funded eductation and old age pensions, and a strong vital business sector to provide the prosperity to pay for all this. He was also the first to popularize the Milton Friedman invented flat tax as a "left" idea. Jerry Brown stole the idea of this as a progressive rather than right wing reform from Vidals campaign against him. (I think partly this may a vague instinct on his part that progressive social spending under capitalism is only possible with a regressive tax system.)
Gore Vidal also underwent at least one period where he was very worried about China as likely to supplant our empire in the long run.
On any issue on which we are likely to actually fight in the two decades he is likely to be on our side. Given his age and health that means we can pretty much ignore any differences as irrelevent...