Stick the headlight in the oven for a while.  This will soften the glue behind the glass lens and allow you to pull it off relatively easily
 

Howdy all,
I too prefer the look of the square headlights and like most, wanted more light and considered getting rally lights for this reason (and 'cause the look great!). But do they...?
Round rally lights with square headlights.... I does look weird. Weird that you can get used to, but be prepared to hear about it from almost everyone who has had an Escort at some point.
If you decide that modifying the existing square headlights is too much bother, you can just buy inserts or conversion kits. From memory, I used this one from Narva; good light and bulb temperatures (Halogens normally get a bit hotter than the incandescent counter-parts).
Cheers!

Gdub
 
The new Narva 7" round conversion kits have a free-form reflector and lens that will provide a much better beam than the old reflectors and you only need to use standard wattage globes which means less heat and less current draw. Fitting these lights with a decent +100% globe (still standard wattage 60/55W) will make such an enormous difference to what you currently have you wont know yourself!
 

 
Gdub, I used the Narva kit on my MK1 and it has made a big difference.
http://www.classic-ford.o...x?m=31446&mpage=12
As many have said there's not many options for a quality rectangular replacement (most are crappy aftermarket which I've read complaints about)
 

hendo
Like you, I much prefer the square headlight, every man and his dog has a round headlight MK1s in the UK, however only 1300 GT and Twin Cams had square ones. (I know its just the opposite here in sunny Oz, but still).
 

 
I think the iconic significance of the MK1 Mexico & MK1 RS1600/2000 is the reason a lot of aussie escort owners make the change. Round or rectangle, both look good with 1/4 bumpers :)
 
 

I went with round because they are lighter and easier to replace in the race car! But the grille is much more expensive and harder to come by...snap!
I also prefer the look though.
 
JP