the tracked sled mystery has been solved, a chap on hmvf posted this pic which pretty much nails it. unfortunately the rest of the tracked sled i bought is at nelson green's yard as i couldn't transport the whole thing in my van. the good news is i now have a daf 4 tonner and the next time i'm over that end of the world i'll pick them up and restore at least one.
quite fitting that an ex REME fella like myself should end up with them
rick