I would suggest that you need the following for the rear.
Either
2x

http://www.theoutdoorshop.com/Outdoor/P ... uage=en-GB
This is alloy and rated at 18kN ( 2.5 Elises)
Or one of the double eye/jacking bars that Stu is looking into.
1x Rich tow rope (Rich consider climbing rope as it's a smaller dia for the same load and is dynamic)
To link the towing eyes with either of the above I would suggest something llike this

http://www.artistic-sportswear.de/en/a/ ... /throwline
this could be made up much cheaper with a quickdraw

and length of tubular climbing tape with some elastic run through it.
If we use the tubular tape with a length of elastic cord run through it then we could clip it on for track days and clip the centre krab on where the exhaust exits on the S1 to keep it accessible and out of the gravel. I think that if a centre krab is used and allowed to run free then the loads should be spread between both eyes.