I've dismantled many Woodstock series (HP2x) calculators. You do it as follows :
Take out the battery pack
Take out the rear (display end) feet, and the screws under them.
Press on the charger pins with a small screwdriver until they're free of their holes. The display end of the machine will separate when you do this, of course.
Now press the front (0-key) end of the keyboard towards the back (charger socket end) of the bottom case. The idea is to slide the keyboard slightly towards the rear end. This frees the hook at the front end. Separate that end too
Slide the keyboard back towards the front end of the bottom case so that the battery contacts fit through the holes in the bottom case. Remove the bottom case completely.
Unplug the logic PCB from the keyboard, unplug the display from the logic PCB, remove the black fishpaper insulator from the battery contacts.