So..... swapped my 120,000 mile engine with a blown head gasket for a 99 with 30k, and no problems that I aware of ( knock on wood). When doing the swap found that though the engines are both the 4.0 V8, the 98 has some variations.... The oil pan is smaller on the 98, the oil filter is at a different angle, there seems to be an additional water outlet with a sensor, that on my 99 engine looks like it has a bolt in it, and I dont have this additional sensor. Got the engines swapped, the new one fits, but with the timing cover, my water pump off the 99 engine is about 2 inches off from lining up with the rest of the pulleys. What is the best way to finish this swap? Are there any other differences between the two motors that I have not yet found that will cause issues? Thanks.

 

Your donor engine is a Bosch engine and not a GEMS engine.
The GEMS is what originally came in your truck.
Why didnt you just replace the head gaskets? $500 and a long weekend and you're done.

You need to swap the front cover, water pump etc.

 

GEMS vs BOSCH Engines - Discovery I, Series II, Range Rover 4.0 & 4,6 - Tech Tips at RoverParts.com

Both engines look like the one on top and the stamps on the side of the blocks read the same. At this point, I think it is going to be a matter of swapping the timing covers and some components. I didn't know if anyone could point out any more issues I may run into or if there was a simple solution....

I was originally going to do the head-gasket job but I found this motor on ebay for 850ish and it was local. I figured I could swap them, do the head gasket job on the old motor since I had it out then sell it.

The swap was easy and I thought I was home free until I went to put the belts on and saw the difference in where the pump sat.

 

There should be zero difference between the 2 engines.
If they both truly are GEMS engines.
Just swap over whatever you need to.