Why oh why do people get this crap mixed up?

The 5.9 Mag motor is NOT internally balanced. That isn't even worth discussion. But it will work with a 318 or 5.2Mag torque converter if you use the 5.9Mag flexplate, because the imbalance is built into it.

RE: altitude...It's a fact that horsepower decreases by nearly 20 percent going from sea level to 6000 ft.

No amount of tuning can replace the lack of atmospheric pressure that pushes the air into the engine. You flatlanders should also be aware that octane numbers are smaller at altitude because the engines don't need as much to run without knocking. So what is 87 octane at sea level is 85 at the pump a mile up.

With that in mind the advice to turbocharge isn't as far out as it would seem.

The best choice would seem to be either Mag engine, maybe they are becoming more available there. When I lived there a few years ago prices were too darn high.

A cheap alternative would be to advance the cam 4 degrees as suggested above, and stick on a pair of junkyard 302 heads, still probably sitting in that maroon '86 Fifth Avenue in the junkyard. Or maybe you'd prefer the blue one. Or the white one. Spend the extra few dollars and use the Mr Gasket thin head gaskets. The combo will raise your compression by at least half a point, and going from 8.0 to 8.5 can really help.
Don't rebuild the heads, just replace the valve seals and slap'em on and see if that helps.

If you stumble across a pair of Mag heads you should know it is possible to use your intake on them by elongating the bolt holes and making angle spacers. If you have an aftermarket camshaft the odds are at least 10-1 that you already have the right lifters, just need a set of pushrods with holes in the ends.

And for those of you suggesting 308 heads, forget it. They are almost impossible to find and they have the same chambers as the heads he has now. Not worth the effort.

So either do the JY 302 head boogie or else look for a Mag motor that you can swap in, most of the other suggestions will cost more than they're worth, or else put you walking for several months.

One other thing - Distributor advance curves. A properly set up distributor can wake a motor up with no other changes to the motor. That should really be the first thing you do.