There is a bit on it here:
https://en.wikipedia.org/wiki/Mattel_Aquarius
Its colour (16) basically a Z80 running at 3.5MHz same as My Nascom
All the analogue 625 stuff is my flat I did find a possibility an old flat screen looks old enough.
Never bought a ZX81 although there is a few kicking around keeping doors open
Will see if I can find the cables tomorrow, its a war zone up there
Cheers
Mike T