I have a slight tapping noise in my engine I think it’s a lifter but not sure in my 1986 xj6 4.2 and it is a California emissions car too if that means anything

 

a Tappet Holdown kit is installed in the exhaust side of the cylinder head to reduce this noise. Most of our cars have it installed already.

It entails brackets that prevent the tappets from moving. Self-tapping bolts drill into the aluminum head to hold the brackets.

not a difficult job but a delicate one that requires precision and total cleanliness to prevent aluminum bits from entering the engine after drilling the bolts in.
Best done by someone with experience.

Go to SNG Barratt USA or UK online store, select year and model, then search for "tappet holdown kit".

Also you can check if your cylinder head (exhaust side) already has it:
Remove the oil filler cap;
Shine a flashlight inside to see if you have a bracket with bolts holding down the round tappet under the camshaft lobe.