Amiga Format also found difficulty installing the CV64/3D scan doubler. They suggested popping the scandoubler card in first, then the CV card over it, then slipping the link cable between them. They also advised leaving the backplate off the cards.
If you're having that much trouble putting cards into place, your daughterboard could be damaged. My father's A3000 bus is slightly warped, so getting cards in and out is a serious chore. If this is the case with your system, a replacement 4000 busboard shouldn't cost more than $30US (?) secondhand. Or your could replace it with a dual Zorro/PCI bridge from Elbox.
