The experience has been that AC Delco modules are the only
way to go. http://www.rockauto.com has them, as well as
http://www.gmpartsdirect.com but the later site is known
for exhorbitant shipping costs.  

Changing is fairly self-explanatory, basically you remove the
distributor cap, underneath is a black module held in place
with two 5.5 mm screws. After removing the screws the module
lifts slightly and then pulls out a bit, giving you room to
disconnect the pigtail that runs to the pickup coil. You
clean all of the old heat-sink grease off then apply a dab
of new grease (use the white stuff sold at Radio Shack and
other electronic suppliers), spread it out evenly and not
very thick, then install the new module.

You can take the old module to most auto parts stores to
have it tested.

JazzMan