I've noticed lately that I can't just compile and install custom blocks and have them show up in grc. I've had to add a GRC_BLOCKS_PATH environment variable that points to the location of my custom blocks folder to make them discoverable.
Isn't the sudo make install process supposed to copy the required files to known places that gnuradio can find them so I don't have to worry about this? For example, I do see the custom blocks .xmls in the /usr/local/share/gnurado/grc/blocks directory after installing.