LSD is manditory but I don't belive they are included in the price. I know some of the options are confusing.
The LPG V8 thing was a mistype by the web developer that was quickly fixed, too bad, LPG V8 would have been excellent, I doubt there is a LPG V8 option being reseached for the Windsor, perhaps for the 5.4L in the AV, but we will never know, not for a while. LPG and IRS are mutually excusive I belive. As are I belive 5 speed and LPG.
I think ford should work a bit more on the specification web thing, some of it doesn't work well, and its sometimes ambigious.
I don't belive you can spec IRS and V8, for that you need a XR8.