No 4 cylinder full of coolant -- help !!!

My P38 started to badly missfire last week and the next day would not even turnover on the starter - I recognised the dreaded 'hydraulic-ing' so did not try again. I took out the plugs and cylinder 4 was full of coolant. With this plug removed I spun the engine to clear the coolant and then started the engine so that I could limp the car near to my garage.

Since Boxing Day I've got to work and, despite the red wine, ruddy exhaust heat shields and the longest breaker bar known to man, finally removed the cylinder heads today.

My worst fears were confirmed when I found no obvious head gasket breaks and could see that there is no water passage anywhere near to cylinder No 4. I've done a lot of searching this evening on rangerovers.net so I think I have big block problems.

My questions is simply this --> is there any point in rebuilding the top ends ? if so how long might it last ? --> or shall I bite the bullet and drag the rest of the block out for rebuild ?

Thanks - and hope you had a better Christmas than me !!!!