As the man who runs (i believe, all) the comp safaris in Scotland - I strongly suggest you come to an event & see what we do, then ask what the various rules & restrictions are.
There are a dozen drivers, who will give you a dozen different pieces of advice... all useful, and all will give you food for thought.
For example, a Supercharger will immediately rule you out of any SLROC championship, irrespective of any other factors.
(On that subject - WHS 423 looks an "interesting" vehicle: what was it built for? The winch & tyres suggest playdays or winch-challenge events rather than comps...)