Even if the liquivac could empty the system, it is not like draining the oil. The system needs to be thoroughly flushed or it's like washing your feet, then putting on dirty socks.
Luckily on these cars, it is very easy to thoroughly flush everything. Remove the hose at the rear, drivers side of the head and the hose from the aux pump to flush the heater core. Open the drain plug at the rear of the engine below the exhaust manifold and then flush through the rear of the head to the drain plug. This is after draining the coolant via the drain cock in the block and the drain cock at the bottom right (passenger) side of the radiator.
Finish flushing by connecting a hose over the block drain and flush through to the drain cock on the radiator.
A thorough flushing and fresh antifreeze is very necessary on aluminum head cars. Mine was not done by the previous owner and the head corroded through. Luckily, my machinist welded it up for me.
Flush that coolant and change it often,