There is an overhaul guide online, and a manual. Search Discovery II Rave Manual and Download it.

You may end up lucking out, and find one that already has a tophatted engine and is sorted out. Who knows, but I think the moral of the story is to really pay as little as is possible for a runner with an original engine due to the posters on this boards past experiences.

We can't predict the future, so take the advice for what it is worth. Just make sure the driveshaft is in good condition and buy an obdII tool to monitor temps. If you find a runner you are happy with just be happy with it.

It would just be really really nice to find a DII in good exterior/interior shape with a blown head gasket someone has given up on and either rebuild or drop in an engine upgrade.

 

I bought my 04 almost a year ago.
Ran great, didn't heat, but ticked loudly.
Interior is great, but needs headliner, outside looks great, cold ac.
New pads, rotors, mc, radiator, waterpump, 20" RR wheels/new tires, that PO put on, and ps pump had just blown.
I overpaid, $3k, but it's black on black 04, what I wanted, and had been looking for, for a long time.
I didn't and don't mind working on it, although, like any vehicle, it can be frustrating. Fortunately, they are very easy to work on.
I hoped the ticking was an oil pump, and it was...and the crank, rod, and cam bearings were shot.
Machine shop honed cylinders, polished crank, installed cam bearings and freeze plugs, and I bought stock rings, bearings, reman heads, measured, and reassembled, just have to put engine in now.
I need to put seals in transfer case, muffler/tailpipe, 4 O2's, all gaskets, change all fluids, UG and Nanocom, ps pump, steering box and rack, pb booster, all of which I've already bought.
I've done a couple window motors and regulators, needs a couple door lock actuators.
And, about 40 things I'm forgetting.
I have a love/hate relationship with this thing.
What's my point? These project trucks can snowball quickly.
I planned on a $3k max budget for parts.
A year later, I'm pushing $8k, in parts.
I do my own work, and machine shop was $375.
The engine itself has cost me over $2k(eating my lift, wheels, and AT tire money).
In hindsight, I think I could have bought a $500-$1000 overheated D2 and spent the same in parts, but oh well.
I would have paid $1500 for the white 04 linked to this thread...until I saw possible flood damage.
That can be an electrical nightmare that is never fixed.
Anyway, keep looking, and be willing to take a road trip for the right one.
I have seen at least 10 D2s since buying mine that are under $2500, and in good shape, regardless of typical LR problems.
I knew if I thought about it too much I'de come to my senses and not buy one. But, I'de wanted one for many years. When it comes to D2s, you have to be willing to fix whatever, whenever.
Good luck with your search.