Will xke headers fit on my 86 sIII

 

Sorry, what is a header ? I'm English so maybe its an American term.

 

The exhaust manifolds with individual pipes instead of one molded cast iron manifold (yes it is an American term)

 

Are you talking about the long sloping aftermarket ones? If yes, I would say no. Visually the E's are too long in a downward direction. It would probably be obstructed by the XJ's suspension and rack.
This is just speculation as I've never tried it. I have thought about it though....Much easier than making custom headers.
(I have seen a shorter interpretation of the e header. It was very triangular like. I have no idea who made them if they were custom or production).
The stockers would probably fits.