Hi Erik,
From your post I am not sure if the steering has just become heavy or it always has been and you have decided PS is the way to go.
If it has just become heavy it could be that the box needs lubricant or that the centre arm needs attention, for the latter rebuild kits are available.
However if you just want to go the PS route, you have several options -
The LX models of 84 had PS so you may be able to locate or buy new.
BJ42s are, I think, 12 volt so the electric PS from a Opel/Vauxhall could be fitted. Although I have never done this, I understand that the electrics are reasonably basic and am aware that this kit is used by the hotrod guys.
Whereabouts in Spain are you? We live in the Alpujarra.
Regards,
Rodger