Replacing my engine...
 

I have a crack in my block at cylinder 6 on my 2004 4.6. Quickly overheats due to the pressure in the cooling system. I've decided to order a Turner 4.6 with Kent cam and gas flowed heads, complete with new front cover, oil pump, and water pump. I'm going to replace all cooling hoses, reservoir with cap, radiator, coil packs, wires, and plugs. I feel this will make my Disco as reliable as possible going forward. Anything else I should replace with the new engine? Am I crazy or smart to go this route? Thoughts or advice is much appreciated.

Long tube headers, professional tune.

I don't think I'm going that far, but that did remind me to order exhaust gaskets. Lol.

Don't see much point in changing the cam and up flowing the heads if you aren't going to get rid of the restricted exhaust and tune to compensate. Leaving a bunch of performance on the table that equates to wasted money.

If you really are willing to do buy that expensive engine & make it most reliable, then don't just buy a new stock radiator, which will not be sufficient in hot weather going uphill, instead buy a much larger capacity all aluminum radiator & instal a inline thermostat as well,,, with this 2 upgrades even a stock factory engine (if in decent shape) will last for a long, long time,, & for a expensive engine like the one you want to buy is the cheapest insurance,,

thats like 8 times more than i have in my rover including lift and tires and purchase price and doing the head gaskets myself. lol, but she will be nice!

Can't go wrong with a Turner engine. Cracking a block has always been my worst nightmare, so this should theoretically take that out of the equation (well to be technical, you can still crack the block, but the flanged liners will stop coolant from going anywhere it shouldn't). You can always upgrade the other stuff later if you want.

I already have too much time and money in my Disco to scrap it. Just when I got it where I wanted it, along came the cracked block with no warning. My whole cooling system had no more than 30,000 miles on it and the oem 180 thermostat was a year old. Always ran 188-194 consistently. Only saw 200-206 at idle in 85+ outside temps. At this point, I want a reliable engine.

Dang, I've heard of a block cracking within normal operating temperatures.

Ditto the long tube headers. Hedman's cost about $228 on amazon last I checked. You'd just have to have an exhaust shop bend up some exhaust for you. They were a big upgrade for me. I definitely still saw a performance bump with just the Kent cam and ported/polished heads, though.

You can also build your own CAI intake tube. Check out my signature. The pod filter isn't necessary; you can connect it up to the factory intake box and still see a little power increase.

Sadly, nobody in the states actually tunes these engines. The Bosch ECU is evidentally a PITA and ordering a tune from overseas is $$$.

I will second the in-line thermostat recommendation. One of my favorite mods I've one to my Disco.