High level description here: Changing spark plugs and wires in my 1996 Express was an all day project for me. It's been a few years, but I recall I had to take the front wheels off to get access. Be safe. I needed to get s 3", 6", and 12", socket wrench extensions as well as a universal joint. I'm pretty sure I used 1/2" drive sockets.
The motor cover in the passenger compartment needed to come out to get access to the distributor. I do not recall whether or not I got access to the rear plugs from the inside or outside.
I couldn't fathom why a garage wanted over $500 to change the plugs, wires, distributor cap. After I did the job I understood. Good luck!