disconnect the pipe from the metering head and the injector and just blow through?

As it's a K-Jetronic (the K stands for kontinuierlich = continuous) all injectors will get the same amount of fuel at the same time. So you can connect the injector pipes to any ports of the metering head, it would make no difference. To make sure it's not the head itself just disconnect the not working pipe/injector and connect it to a different port.