[AMSAT-BB] Advanced Receiver Research MSP144VDG-160 mast mount cover removal question

I have an Advanced Receiver Research MSP144VDG-160 mast mount preamp, but it does not seem to be configured to be powered via the coax. I removed the cover screws, but the cover does not seem to want to come off easily. Does anyone know if there is some trick to release some sort of latch or something so I can get inside and add choke and/or capacitor? Or should I just pull it off more "enthusiastically"?

de KM1P Joe