Overheating one time is enough to drop a cylinder liner and/or warp a cylinder head. On the 4.0 check for head warping and seeping around liners on the cylinder deck of the block. On the 4.6 additionally check for cracks around the upper cylinder head bolt holes on the block. I don't bother with the torque to yield cylinder head bolts, I use ARP studs instead (there are folks who say this is not needed, but I don't like doing jobs twice), the Buick 215 studs are cheaper than the Land Rover studs (you just get some extra studs for the lower deck holes that new type Rovers don't have). I also use spray-on head gasket sealer (again folks say it's not needed, or desirable). Use a thread sealer on the head bolts (blue Loctite is good). I did this on a 4.6 a couple years ago (with cracked bolt threads) and my 3500S many years ago and all is still good. On the 4.6 CRC sealer ended up being used due to leaks caused by the bad bolt threads in the block. If the heads are warped (and I bet they are) a good automotive machine shop can fix them up. If a cylinder liner has fallen out of place, that's a whole new can of worms...

'99 Disco II
'95 R.R.C. Lwb (Gone...)
'76 Series III Hybrid 109
'70 Rover 3500S