[webbee]

I've only done the rear plugs from below, with the front end up on ramps. It takes some creativity with swivels, extensions, and your hand/arm in some tight conditions. You will also need an 8-10" piece of hose that fits the plugs ceramic insulator to make installation of the plug into the head threads easy.
Others loosen/remove the alternator and get all 3 plugs from above with out removing anything else. I've never tried that method, so I can't comment. You probably have to remove the serpentine belt to deal with the alternator, which adds work time to the project.

Be careful removing the plug wires as you can break the core, which will cause missing. There is a plier type tool that removes plug boot/connections easily. If your changing wires too, I would change a plug, then it's wire, until I was done. Watch for binding/touching wires around the rear head, behind the alternator.
Always use copper anti-seize on all plug threads. It keeps them from galling/welding themselves to the head. Di-electric grease in all the boots keeps moisture out and aids future removal.

I use NKG platinums and like them best for replacement plugs on the 3.3/3.8. Others use Autolite or Champion Platinums. Make sure you get double platinum plugs. Copper plugs work too, just not as long. So...thats why I use platinums because this job isn't too much fun.
Plug gap is critical, be sure to set it to factory specs for your engine.