Just thought I would add to this with the information I have been able to find, still haven't got a definite brand which could have come out on the MK1 Escort. 
 
Seems that the MK2 Escorts might have often came out with the Goodyear Supersteel tires from what others are saying but can't find any information that they could have come out with the MK1 also. I went to a Ford dealership today and asked the parts department whether there was any possibility they knew what tires the MK1 Escort came out with. I was told that Ford's major tire contracts are with both Bridgestone and Goodyear. I spoke to someone at a Bridgestone store and there are no 12" tires available in either the Firestone or Bridgestone range in Australia. Looking on the Goodyear website it appears they don't sell 12" tires either. I did learn however that 155R12 tires are still available to buy it's just that they wont be your big brand names. 
 
Had a look in the Universal Tyre Fitment Guide where it has listing for the Escorts
IMAG0041[1].jpg
 
I found that one of my 2-doors still has its tire sticker inside the door.  Apparently the crossply range is no longer made but the radial range is. I'm unsure if the 4-door or Panelvan had the same sticker. If people still have their original sticker could photos be posted on here.
IMG_9985[1].jpg

Found this infomation on the link below...
"Tyres on the earlier RS2000 were Goodyear Supersteel radial 175/70HR13 and on the later Uniroyal 180/70HR13"
http://www.rsownersclubaust.com.au/?page_id=1753
 
 and found this advertisement, the Goodyear Supersteel range must have been after the MK1's. I can't find anything earlier.
http://www.ebay.com.au/itm/1977-GOODYEAR-SUPERSTEEL-70-TYRES-FULLPAGE-COLOUR-MAGAZINE-ADVERTISEMENT-/221359356768
 

My mk1 is a 7/73 build, originally a 1300 auto, one owner, with 38,000 miles and still had what appears to be the original 12in steel wheel spare. It's marked Dunlop Guardian 6.20 L12 LP 41, 4 ply rating tubeless. The Tyre ID number is 7Z33462N. From what I can find it was made in China, the last 3 numbers apparently mean it was manufactured in the 46th week of 1972, going by the look of it I doubt that it was any later decade. It also predates my car which should rule out it being a replacement. Although I could be completly wrong A google search shows these being advertised in the late 60's and early 70's. Hope this helps.

Dave.