Well, i was thinking of doing a video when it dawned... heck, there may be already some on YT.
So, some good references about opening the carts:
1)
Opening Your Cartridge - 8-Track Repair
List instructions for Columbia 3-tabs, LearJet 5-pins - WEA twintab and sealed shoud not be ok for you.
2)
Audiopak, used by Capitol and WEA, with or without screw
3)
Riveted cart, RCA
4)
GRT cart
5)
Columbia 2-tabs.
Tip: if you want to open that kind of cart without ripping the cover, there's a way: looks closely between 5:42-5:47.
In order to open it, the top part of the cart need to slide from up (tape/pads/roller) to down (album title) and to prevent that accidentally, there's a thin riser on the down part of the top part of the cart. So,
1) look again at the 5:42-5:47 section above and place two dimes on the two down angles between the top/bottom of the cart
2) open the upper tab with a flat screwdriver
3) now raise the top part so that it can move toward down and slide it toward down; you will soon hear the POP that the covered second tab has opened.
6)
Five hooks
7)
8 track open AMPEX posts type (AMPEX Repair pt 1/3).MPG
Ampex 5-post
Making Foam Pressure Pads for 8-Track Tapes
Making foam pads