Elevation change:jet size change ratio?

I'm driving my 66 coupe, 351W, T-5, 3.50 rear gear From Monterey, CA to Dayton, Ohio with a pitstop in Pensacola, FL this summer(5000 miles). I have a 650 double pumper(Speed Demon). I am touring the country and have plans to hit a few high elevation spots(Grand Canyon). QUESTION: what is the formula for jet size change per X amount above sea level? I'm starting/tuned for sea level and I found the Grand Canyon area can reach around 8,000ft above sea level. I have had bad experiences in the past with drastic elevation changes that cost me a day of travel due to low O2 levels. Thanks for any imput. See you on the road!

Thank you. I will be changing jets on the road. I went out and bought a few sizes to test and tune en route.
I should be in Vegas for the weekend and on to the Grand Canyon Monday and be in Mesa, AZ for a few days before I head out to Dallas etc.