Hi,
You can reduce the mess a little by draining the cooling system as completely as possible first, via the petcock on the bottom of the radiator and the one on the side of the engine block (roughly below the heater control valve, about half the distance to the starter).
Alternatively, just remove the large radiator hose at the bottom of the rad.
In fact, getting a high rate of flow out of this bottom hose might act a little like a siphon and suck more of the coolant out of the entire system. Leave the rad cap on initially and be sure the heater valve is open. Pull loose the hose, and let it flow.
Next remove the heater hoses inside the engine compartment, before those inside the car.
The above procedure won't remove all the coolant from the heater, but will reduce the total amount a bit. I agree with cutting the interior hoses (have your replacments onhand first).
While everything else is apart, you might optionally want to remove the heater control valve and the pipe that comes from the water pump housing along the LH side of the engine for inspection and cleaning. The bulkhead fitting, where the heater hoses attach at the firewall, are prone to rusting and might need replacement, too.
I also feel it's dangerous to use compressed air to force coolant out of the system. There is simply too much danger of doing a lot of damage to a system that basically operates on very low pressure. Damage could be done to the head gasket, the figure 8 seals on the bottom of the liners, the radiator or heater cores, or any other seals in the system. Some of these possibilities could require an engine rebuild to correct. Too risky for me!
Cheers!
Alan