If I remember correctly the weight penalty is around the 350kg mark - remember it isn't just the head and tail but changes to the undercarriage and tie downs etc. Unfortunately unlike the Mk 1 to 2 there isn't much scope for reducing weight as I believe most of the weight reduction in that programme was linked to the mission kit that clearly isn't present in the 3/3a. If you add in the BP fit (a brave man who wouldn't given it is available) + DAS fit you are adding around 900kg to the basic AUM giving 3600 kg (ish, figures from memory only) disposable on a 15,600 cab. So not a performance upgrade but clearly giving it a capability it doesn't currently have. All it needs is a reduced basic weight, better engines & gearbox & we might have a cracking machine!