You're probably overfilling it. There has to be some room for expansion. Also, be sure the radiator cap is right--they come with various relief pressures. Not sure what the TR3 one should be set for, but it will be listed in the shop manual. Shop manual gives 4 psi for the TR4; I assume the TR3 is the same.
Your altitude may also be a factor. At 7000 ft, atmospheric pressure is about 2 psi lower than sea level, and I think Aspen is around 8000, yes? You might need a little higher pressure cap (maybe 6 or 7 psi?) to compensate, but be careful of too much pressure if you visit the flatlands.
If you open both the block and radiator taps, open the heater valve, and remove the radiator cap, you should be able to drain the system just fine. Flush it with water and a radiator-flush substance from your local parts store, following the instructions on the bottle. Then close the taps, keep the heater valve open, refill with coolant, run the car a bit, and recheck the levels. You shouldn't have problems with air bubbles. None of this is the proverbial rocket science.