Our E450 engine is now the proud owner of 10 new spark plugs and 10 new coils!!
As promised, here are my experiences in doing this job. It actually turned out to easier than I had feared. First I removed the seats in the cab to get some room to work. Removing the seats requires a Torx #55 and an 18mm socket.
Access to the area around the coils and plugs is limited but after the heavy wiring bundles that feed the coils, fuel injectors, and other items were moved out of the way it wasn't too bad getting to all the plugs. I did not have to disconnect the wires to the fuel injectors, but did remove the wires from all the coils to get more space to work in. No concern about mixing up the coil wires as they are too short to reach a wrong coil. The cylinders are numbered 1 to 5 front to back on the passenger side and 6 to 10 on the driver's side. I was able to remove and replace the coils and plugs for numbers 1, 2, 6 and 7 from the front and the remainder from the inside of the cab. The most difficult were numbers 3 and 8 because it was hard to get leverage on the wrench in the confined space to break the old plugs loose and properly torque the new plugs.
After the cables and other items were out of the way, I used compressed air to blow as much of the dirt as possible off the top of the cylinder heads and around the coils. After removing each coil hold down bolt (7mm socket and 1/4 inch ratchet worked fine), I twisted the coil and blew off the surrounding area again before pulling the coil out. After removing each coil, I blew out the spark plug hole. I removed all of the coils on the passenger side first, then started removing and replacing the plugs on that side one by one. As I unscrewed each plug, I removed the spark plug socket a couple of times and blew out the hole to make sure no grit got into the cylinder when the plug came out. Overkill maybe, but why not. I screwed the new plugs in just turning the socket extension by hand to be sure not to cross thread. The plugs went in dry, no antiseize. I torqued to 180 in-lb (15 ft-lb). After doing all plugs on the passenger side, I installed the new coils on that side to prevent any grit from blowing off the driver's side from getting into the plug holes. Same steps as above for the driver's side. Now for the pictures.
Cab with seats and doghouse removed.

ZIP ties holding wire cable away from coil spark plug area

Closer view with cable bracket bolts removed

Passenger side from front with bracket bolts removed

Driver's Side front view

#6 and #7 spark plug holes

Passenger side from cab after all new plugs and coils installed

Driver's side with all new plugs and coils installed and wiring cable back in place (tight, isn't it?)

Everything back in place

Motorcraft ignition coil info

Old spark plugs. Gaps were 60 to 75 thousandths with #4 and#5 the worst. New plugs gapped at 54 thousandths.

Tools I used for the job. 1/4" metric socket set not in picture. The magnetic 5/8" spark plug socket with attached swivel extension was the best thing I bought for this job. The swivel made it so much easier to get the socket into the plug hole in the tight quarters.

After doing this once I wouldn't hesitate to replace just the plugs again in 50-60,000 miles.