This is probably the worst case scenario but it can and has been done.
You will have to of course remove a few things like heater hoses, fuel line rail,
coil pack etc. to get to the spark plug which is normal for most repairs.
You may have to do things a little different from the instructions
The instructions say to connect the "wrench tool" to the reamer tool
then place it into the hole. The length of the 2 attached tools is too long.
It would be better to place the reamer tool in the head first then,
you could place the wrench over the reamer so you are not trying to
place a 14 inch over all length tool in the head at one time.
You might want to try an air
This would help speed up the reamer tool process which takes the most time.
There is a 5/8 hex on the wrench tool provided, or use a socket to turn the wrench.
One customer used an offset ratchet where you turn the red handle to ream the hole.
(picture below is a 1998 ford E-350 van)
The method above is just a possible solution to the clearance problem.
You can review the thread repair process again here.