Nikasil are early V8 cars only, these are 1998 - 2000, they are easy to identify. If the car has 6 digits at the end of the VIN# it’s a Nikasil nightmare, if it has 5 digits it’s a steel liner engine. BUT - many Nikasil engined cars had their engines replaced with steel linered units under warranty. Therefore service history and a thorough engine test is critical before you buy a 98 - 2000 V8 powered car.
But an 80’s XJS has none of these problems since it will be either an AJ6 or a V12 power plant, neither of these is Nikasil lined. The V12 is a magnificent engine but can also be a maintenance nightmare with high service costs due to poor accessibility of just about anything. If you don’t plan to do your own work, get a good 6 cylinder 4.0 Liter AJ6 powered car, the AJ is an extremely robust unit and much easier to work on.