It's not too difficult to equip the GRE PSR-282 with a discriminator output. The receiver IC can be located underneath the 10.245 MHz crystal. It's a 3361, with the unfiltered auio at pin 9. There is no need however to solder to this IC. Pin 9 has a direct connection with test point TP5.
Test point TP5
The connection to TP5
Follow the next steps to make a discriminator output: