This is one of my most un-favorite jobs. You absolutely have to do it from underneath or thru the wheel well. Most of the time you have to do it by feel, because you cannot see the plugs. Changing the plugs is not that bad, but plugging the spark plug wire back on, you need to pay attention. I had a wire that I thought was on, but it was wedged between the plug and the exhaust manifold and gave me a check engine light.
Since we are even talking about Astro ignition, these vans have Extremely high voltage ignition and they eat distributor caps and rotors and ignition wires.
I don't buy cheap cap and rotor and ignition wires like Duralast. Pay more for the name brand like Sorensen or TRW. Ignition wires like Autolite and I will only use Autolite double platinum plugs, because I have a problem with new Bosch double platinum plugs.
I wrap my new coil wire with 3/8ths sprial band and co ver the whole thing with half inch split loom. I am careful to route the coil wire not near any engine supports or anything grounded.
I have had 4 Astro's since 1994 and I drive a 1999 now and it has 208,000 miles and I drive it 1,000 a week on service calls.
Been there, done that, bought the tee-shirt, and sold it at a yard sale.