Here's some stuff that ought to help checking the pick up coil.
From the book - I know you hate Vettes mofo, but act like it's out of a truck manual ..
http://img.photobucket.com/albums/v228/Avette4me/Vette/Tech%20Manual%20Stuff/Pickupcoil.jpgHere's is the test item you'll need to make. This is my version of the ST 125. Use the wire to ground the plug and check for spark.
http://img.photobucket.com/albums/v228/Avette4me/Vette/Tech%20Manual%20Stuff/100_1309.jpgIt's pretty easy and you'll know right away.
Good Luck...
Edit - I'm adding this page just in case. I assume you've checked all the other components, but you never know when dealing with really old dudes... :-)
I dispensed with all the dwell and ohm checks. I knew the other stuff was good and when I missed getting spark, I just changed the pick up coil and twalaaa....
http://img.photobucket.com/albums/v228/Avette4me/Vette/Tech%20Manual%20Stuff/pickupcoil2.jpg