I humbly reply with the following info for anyone getting started with this type of project. First, since the asking price of the used 4.6 Bosch Engines (no cast mark of 4.0 or 4.6 on the plenum housing since there isn't one - but, the modern looking intake made up of long tube runners like a GM tuned port engine) is a freakin' joke.... 135K unknown miles & demanding $2500 , 47k and demanding $5k+ .... don't buy an engine unseen w/o the CarFax report documenting the donor vehicle. This will guarantee the '03 or '04 Disco II is optioned w/ the 4.6 or the '00 - '02 Range Rover is likewise equipped.
This type of history is only going to be available from the most reputable Land Rover dismantlers such as motorcarsltd.com , coventrywest.com and their like - only. Or, buying the engine directly from the owner of the donor salvage Disco, R.R. - site seen, Not unseen - with the identifying paper work. The VIN on the block will match the VIN of the donor vehicle.
Simply put, if you don't have exact history on the engine do Not buy it.
Without buying a known donor engine you're not going to be able to pull the heads and observe that the 4.0 has a more shallow dish in the piston top, the rod is longer on the 4.6, or the stamping cast into the piston top identifies the 4.6 from a Range Rover vs. the 4.6 in the late Disco II.
Take your time in planning your engine upgrade and don't get desperate, and commit to the fact that it'll take some money to do right. Minimally, the machining of the block for the replacement Top-Hat cylinder liners.
This is now the step to reach out to Mark Lagrou, D&D Fabrication, aluminumv8.com, one of the finest automotive enthusiast I ever had the pleasure of doing business with. There's going to be a few folks who are going to disagree but, his family is the most knowledgeable Buick/Olds/Rover aluminum V8 expert in North America.
A very expensive 47k mile engine is no guarantee of longevity (ouch! yea, from experience) and has every single engineering flaw of a brand new off the shelf engine that has NOT been re-engineered with modern top-hat cylinder liners, after having the block's integrity verified, squared via resurfacing, cam bore examined prior to the machinist at D&D installing the cam bearings themselves. Fed-X can get your 4.6 block to and from MI (that's Michigan) safely once boxed securely (96 lbs.)
MINIMALLY - rebuild the oil pump, better - replace the front cover with new (Lagrou won't commit to anything other than this option.) Don't even consider using old motor mounts. Buy, the studs & bolts manufactured by ARP for Mark Lagrou's engine specialist (from D&D Fab.)
I am sure I have one of the finest running 4.6 Bosch engines in my '00 Disco II due to the tireless input and guidance from Mark at D&D Fab. He insisted on building a "hood slammer" stage II setup and he was exactly right.
I'll not be posting anymore replies to this note based on my personal experience for the upgrade to the 4.6 Bosch in my '00 Disco II.
The operators of D&D Fabrication (Mark Lagrou!) are the experts and love building the Rover/Buick aluminum V8.
Mark Lagrou's team is the unsurpassed experts. Reach out to them if need be.
Thanks for reading, Mike.