The M103 is the easiest engine to do a coolant change of any car I have ever owned.

There are two drains - radiator (behind the pop out cover under the bumper) and the RH side of the block below the rear manifold. Both have nipples you can attach hoses to for spill free draining.

To flush the engine remove the heater inlet hose from the LH rear of the cyl. head and flush both the block and heater core circuit.

Duke