Where is it ? Are they easy or a pain to replace ?

1985 Astro Mini Van. 4.3 V6

thanks in advance

I am afraid it is in the fuel tank, you have to drop your tank to get to it,
yes it can be a pain if you don't have the right equipment.

Tableman, do you know what special tools I would need to be able to do this in my driveway ?

High jack stands, to get the van up high enough to pull the tank out once you have removed it. And hydraulic floor jack on wheels to help you lower the tank and pull it out with out holder the weight or letting it drop to the ground. Other then that standard tools