I'll check my shop manual for a '99 4.6L tonight. I have the manual
for a '00 4.6L here and anti-seize is not called for. The torque is
specified as 20 Nm (15 lb-ft) and the dielectric grease is listed in
the items required box. There is no mention of anti-seize.

I also sent a question to NGK about anti-seize and got the following
response:

.....

Ed,

It is typically not recommended to use anti-seize with our plugs as
the compound can act as a lubricant during tightening and cause
excessive torque and possibly plug failure even if the correct torque
is seen with the torque wrench.

The trivalent metal coating (zinc chromate) that is on our plugs is a
very non corrosive/resistant metal and is usually all that is needed
to resist corrosion and seizure. If it is an application where there
may be a lot of water getting into the plug socket or the vehicle is
known for corrosion or seizing plugs then I would suggest to use a
very small amount of anti seize and be cautious when tightening so as
not to over torque. Hope this helps, thank you.

Best regards,

Brandon Peeler

Technical Support Representative

Aftermarket Division

NGK Spark Plugs (U.S.A.), INC.

........

So I guess this is a mixed message. It seems like NGK is saying, you
don't need anti-seize, but you can use anti-seize if you want to and
if you are careful. Autolite was more negative, saying not to use
anti-seize, but their concern was excessive anti-seize contaminating
the insulator and shorting out the plug.

Ed