Keeping the stock curve and changing your fuel with altitude isn't going to be a great solution. Without EGR, the problem isn't that the stock curve is too much advance at all engine speeds, but rather that there's too much at some RPMs and too little at others. That means if you adjust the timing for one part of the range, it'll run okay in there but poorly in elsewhere; you either get pinging under some conditions, or you have to set it so it won't ping at all, which means it'll be running without enough advance through most of the RPM range, and only 'just right' in a couple of particular spots. Result? Smelly exhaust, less-than-ideal MPG/power/torque. It'll run, though (mine has been desmogged with a stock distributor curve for 7 years now), just not ideally.
Now, re: altitude, I've found that my setup runs about the same (reliably 'okay') from sea level up to ~7000 feet, and the timing not being advanced enough up at 7000 probably has a lot less effect on the running than there only being ~78% as much air at that altitude (since it doesn't have any sort of turbo to help with that).