It's funny anyone would put a cone on that even thinks of off-roading. Matt, chime in here! But almost every Rover mechanic/owner/off-roader I know SWEARS by the oil bath as being the best filtration hands down. Keeps the intake as high as possible in the truck, without going to snorkel. And keeps all dust/particulate matter out of motor, without exception.
15", especially galvanized, sounds aftermarket. Maybe U.S. dealer trying to make tire selection easier for U.S. owners? Matt???
As far as diesels-
I bought a shortblock, with diesel pump, and .090. overbore off eBay out of Boston about two years ago. Got it for 75.00, and had my mom bring it to Florida to save shipping. In the back of her freelander, it sank the rear suspension, it was so heavy. Thanks, mom! Knew there was a good reason for you coming down every year for xmas! lol!
When I went to buy a head, could only source one from the UK, and to ship it cost more than twice the cost of the head because of the weight. So I said screw it. It's been in the same shipping crate now, (shortblock) since I bought it. Every couple of months I throw a spanner on it and turn the crank, introducing more Marvel into the bores. But I will probably never build it up.