In my opinion to radically alter a vehicle like this (especially as you say its resonably tidy) is wrong!!!
There used to be quite a lot of these on the circuit a few years ago (in fact I owned one) but you dont see them very often now.
There are a couple that have been painted in "garish" colours and used by the owners as motor homes, but to see one still in Civil Defence colours is rare and they do help to illustate an interesting time in our recent history and an organisation that was set up in case of nuclear war
Quite a useful vehicle really can be converted into a camper without ruining the exterior appearence and if fitted with the cost cutter engine quite economical (oops just seen yours has the V8, still a very nice engine though)
The gearbox though is an aquired taste!!