Hi, Are Twin cam rear arches different like the front arches?

Same as stock escort. ..However there are some that say they are a little wider than stock , as with the RS2000 mk1 rears being wider. They only ran with 13x5.5 rims and 175-SR tyres ... Plenty of room without modifying.

I have picked up twin cam front guards and thought the rears looked a little small. I did a google search and didnt find much, the only thing I found was maybe the rears were 20mm wider. Its going on a Esky van I'm building up.

I don't think ford would change the whole rear quarter die stamp for a little clearance .
The rears don't need to turn so they can be small . I Modded my replacement escort rear arches on my van to look a little bigger before welding them in.

Your van looks great, thats the sort of look I am after. Something that matches the front. I have Capri struts that I will be using also.

Thanks ! The van was ready for the scrappers but being an ex yellow RAA van with some history i decided to save it , it was rusted very bad , bashed and crashed over its 40yrs life ! So i restored it and painted it Ford RS Performance Blue .
Here is the front pic

I was thinking of going to the Mexico front as well but now new panels cant be purchased in Oz I changed my plan. Between buying the van and starting the build the business selling the panels stopped supply.  I did have a Mk1 van near new many years ago, it was orange with GS stripes,  spot light grill and sports wheels factory fitted. From searching google I believe it was a factory GS van. 

Rear arches are standard on twin cams. For the front either contact one of the many small Ford specialists or you could buy reproduction Twin Cam front arches and graft them onto the standard van guard. This is what we did on my Sundowner. I'd like to post a picture but apparently now you can no longer just copy and paste into the text! Cheers, David.