Jim,
Not knowing how you measure or track effective air density, I can't gear my response to your technique. As a starting point air density at Bonneville is ~ 16% lower that at sea level. So I would start with 10% less jet AREA. Then read plugs (you strike me as an "old school" type). If you have equipment to measure atmospheric conditions all the better. Hope this helps.
x2Jim,
Whether your tune at your normal density altitude is "tight" or "generous", when you go up in altitude you will typically be rich(er).
One of the things I advise carbureted guys to do is to calculate the difference in jet
area, from one jet step to the next. These steps will probably
NOT be uniform.
You will then need to calculate the density altitude for your regular conditions. Then figure that the D/A at B'ville varies, from say 5500 to 8000+
Calculate your % change and you need to change the jet area somewhat less, say 5% or so. Because of the varying conditions you
will need to have a selection of jets in your tuning package. Change and tune in conservative steps. A rich running engine is much better than none. Checking your plugs after jet changes is a requirement to keep your engine intact.
Fordboy