Nice looking truck, the mileage might be gallactic but if they are motorway miles and the motor has been service properly you shouldn't have any major issues, just stay on top of coolant and oil changes.
From the photo it looks as though it has had a lift and bigger tyres! If not the Deli site recons you can fit range rover front springs on the rear to acheive a 2" lift, tweek the torsion bars up on the front and you cn get 265/75R16's under it.
If I can find an L300 manual for the right money I'll be following in your footsteps so to speak, for info purposes the L400 (yours) in SWB has a wheel base of 110 inches same as a Landy 110, the LWB L400 is somewhere around 118 inches.I want the L300 as it has an 88 inch wheel base and with the right diffs you can get lockers. With a 2.5 inch lift it can also squeaze 265/75R16's under it with out having to do much in the way of trimming. Down side is it is onlya 2.5ltr engine producing around 85 bhp. The 2.8 ltr in the L400 is circa 125 bhp.
Anyway enough of my ramblings, good luck with it and keep the picks coming of what you are doing by way of mods and outings on the lanes.
Regards
Stuart
Remember, keep the greasy side down!