I agree with RRToadHall that you need to start from scratch - at least back up a bit. For now let's assume the engine is good per the place that sold it to you (really you have no choice as the original intake, injectors ... are in an unknown condition - your situation is not optimal), but I would like to know when it was run last as there is gas in the rails and this could be bad. So moving along this line of thought let's move forward.
But before moving forward I want to warn you that damaging the engine in a no start, but turns over, condition is possible. If you are spinning the engine and it is pumping gas you could wash the cylinder walls and trash the engine. Been there and done that, actually my wife did it for me. So be careful. If in doubt smell your oil for gas, and maybe add a tiny amount of oil into the spark plug. [Note: What you described regarding the original engine - scored walls and metal - could have been caused by the same condition you are now struggling with - although it is possible it was caused by timing chain guides - Again Warning! To be safe you need to get everything in order without turning that engine over too much. This means figure out your fuel supply issue - whether wiring, fuel filter, fuel pump, fuse, relay and/or ?]
First let's start with the easiest possibility - the gas is bad. How long has the gas been sitting in the tank? If the gas has been there too long this could be your issue. Related is the gas that is in the donor engine fuel rail may be stale. Generally gas will work for a year or more, but it is something to think about. From what you say your issue is most likely not stale gas. I would think on these lines if you have running issues - but something to think of in the back of your mind once you get it going.
You state that your fuel pump is not turning on. You did some jumper work and concluded the pump works. So back up and check your fuses and relays. I believe the relay can be swapped with the one next to it in the boot. Do some research and confirm. There is a good video on YouTube where the poster walks through his testings - watch it. I have included some postings similar to yours below where members work through their similar issues. After reading these and watching the video, one contains a pretty good explanation of the system operation, you should be able to diagnosis and repair your fuel delivery at the pump. You need to get your fuel system working correctly - no jumper rigging - that way you can move on to the next potential issue. Right now you know you have a fuel delivery issue - solve it first.
Next go to your fuel filter - it could be clogged. Its age and the extended sitting may have done it in. Just change out the fuel filter to take it off the list, they are not too expensive and unless the thing looks brand new the fuel filter maybe the original 15 year old filter.
Here are some links to look at.
Check this cable near the battery: http://www.rangerovers.net/forum/6-...1481-next-step-crank-but-no-start-03-hse.html
See here for this guy's trouble shooting: http://www.rangerovers.net/forum/6-...ange-rover-fuel-pump-electrical-problems.html
See here pump and filter http://www.rangerovers.net/forum/6-...866-03-hse-died-highway-fuel-pump-filter.html
Work through these items and report back with specific issues and failures - with this approach it will be easier to help you.
It is possible the original engine died because of oil starvation caused by failed timing guides. (It would be great if you could look into this as it excludes other possible issues. Engine #2 on my RR met its death in this manner, while Engine #3 from cylinder wall wash -- both had scored piston walls but for different reasons. Dropping the oil pan of the original engine will reveal if the original engine died because of failed timing guides as it will be littered with plastic pieces some in the oil pump pick up screen - ask the shop if you cannot go back and look or you may know this when you did the oil pan swap to the 540 block) Back on topic, if the original engine failed due to timing guides you can assume, with greater certainty, that the rest of the RR is operative. With this assumption you can focus your diagnosis on the electrical portion of fuel delivery that may have been taxed by trying to start an engine that will not start. This would be fuses and relays.
One other place you may have a problem is if a rodent chewed through a wire related to fuel delivery. By working through the diagnostic tests this will reveal itself.
By starting from scratch and going through all of the diagnostics in an orderly manner, removing items once they properly pass testing, you can focus the forum's resources and help you work through the roadblocks.
After you get fuel delivery solved - next step will be to look at your injectors, but for now it is assumed they are working as the donor engine ran.