Thanks Paul.
 
I have two spares which, from memory, never worked consistently. I think I will try to do some testing before taking them anywhere.

The wires on my sending unit are broken. I've put it back in the car for the time being.
I did look for replacements and Jeep sender units on amazon were around the same ohms and had both the fuel send/return lines.
Was considering taking a punt on one of them, just need to size a few up to get one that matches our drop tanks.
Example: https://www.amazon.com/MTS-JPSU-3-Jeep-J-Truck-Sending/dp/B008SH4BXY
 
I did have one saved that was a perfect match but seem to have misplaced the link... 

I have noticed reproduction units for XB/XC Falcons on eBay and wondered if they could be adapted to suit an Escort. The pick up pipe would have to be cut down and possibly float level adjusted but given the XC Falcon is from the same make and era perhaps all else would work?
 
https://www.ebay.com.au/itm/FORD-FALCON-5-16-FUEL-TANK-SENDER-UNIT-SUIT-LATE-XB-XC-SEDAN-COUPE-STANDARD-TANK/331902500136?hash=item4d46ee3d28:g:Wv0AAOSwzJ5XffQM