Nicasil is the cylinder bore lining--has nothing to do with the heads.
The problem with Nicasil was that high sulphur levels in the gasoline scarred the cylinder walls. I personally presume that sulphuric acid was produced during combustion and ate the nickel plating that holds the lining together,
Two quick tests:
1) Open the drivers door with the car idling in gear and the brake on.
Is the top outside corner of the door visibly moving? If the answer is yes, it has a vacuum leak - some causes of vacuum leaks have simple cures.
2) pull the passenger side (LHD) spark plugs. If the two back ones are black and oil wetted the motor has the nicasil pitting problem. The only resolution is an engine block replacement or sleeving the block.
There are fancy tests to do the same thing but they cost money with no better answers.
Test one is actually what a dealer will do first to see if it is a vacuum leak versus just normal wear. Then in the US at least he will hold out his hand and ask for about $13,000 to $14,000 US to fix it.
If he is running non synthetic oil then putting in a heavy synthetic like Mobil 1 15/50 will minimize the smoking.