The only way to know for sure that your ign box is 'fine' is to.....substitute it with another one that you know works.
An MSD coil I bought a couple of months back is made in China. Well that is what the sticker says!!!
Very good advice above to use your dist to trigger a GM HEI module. Dead simple to hook up, cheap, big high energy spark. Get an E core coil to use with it to get the most out of the system.
When everything running the spark is fine, the car runs like freight train. Which makes me think it's something else. It is possible the box is the problem, but with all of the other variables I'd like to see if there's something else first.