[T2] Carbs and change if altitude

[Greenhouse guy]

I have a 1600 DP, in my bus.  I live in Texas at a altitude of 3200 ft.  Question is what do/can it do when traveling to higher altitudes, such as 8000ft?  I lose a lot of power up in the mountains.  Back when I had my stock 1800 with stock dual carbs(before I burned it up), I was in the mountains and could barely pull out on the highway in town.   Do I adjust timing?  Adjust the carb? 
I'm considering building up my original 1800 type 4 motor and adding FI, but that all is pricey.  

Richard
Lubbock, Texas
1974 Westy