I have these heads on mine and they are a pain as far as plugs go. I have socket that I cut about 10mm off so I could get it on no. 3 plug I think then I use an open end spanner on the hex of the socket. A longish plug boot cut off a lead can be useful for starting the plug by hand as its flexible but can still be rotated with the plug in it.
However, my number one tip is to invest in a good set of iridium plugs so that once they're in you don't have to ever do it again. That's what I did.
If you open the bonnet of a new Mustang you might wonder how they get at the plugs on those too.
