In 3.7, you would use the <nports> tag, but in 3.8 the trick to setting multiple ins/outs in the YML file, is the keyword "multiplicity". You can see the details of how to configure here: https://wiki.gnuradio.org/index.php/YAML_GRC
YAML GRC - GNU Radio<https://wiki.gnuradio.org/index.php/YAML_GRC> Starting with release 3.8, YAML replaces XML as the file format for GNU Radio Companion. This is triggered by switching from Cheetah to Mako as the templating engine, since Cheetah does not support Python 3. wiki.gnuradio.org
