All of them are ok (eBay links sent in PM) to be use on the Zx81 and the Spectrum!
Just count the pins on the connector, 23x2 for the Zx81 and 25x2 for the Spectrum.
If the card is ok for both computer, the socket is a 23x2 (zx81) socket.
Have a look to the KEY (the little peace of plastic in the socket!), count the pin column.
2 for the ZX81, and 4 for the Spectrum.
If a Spectrum card is a Zx81 socket (2 pins at the left of the socket key), it will work on both computers !
Note: An7805, your PM is disabled !