Simple answer for 24 volt think 'Truck'. Most things are available, though may cost a bit more. Still far easier to live with 24 volt than try and convert. Check fuel and oil levels before starting! You have no idea what's in there or the crud it may have acumalated. Most parts such as fuel fliters etc are the same as civvy models. If the engine turns over and fires Whoppe! Switch stright off, change filters and oil then restart . Would be very wise to change cam belts as well. Not sure if the Wolf engine uses one, but Land Rover engines in genral are a bit notorious for running till the belt actually goes and causing a lot of headache. Good thing is not a bad job to do, and you can forget for 50,000 odd miles.
Quick check says the engine is a 300tdi. Having just done the cam belt on Number One Son's Discovery TDi 300, a piece off p**. Kit costs about £135 including all gaskest and new idlers.
Just asked son. Proper Land Rover cam kit was £120, though cheaper kits are available.