Supereal's comments are right-on.
My '47 59AB 12 volt engine came to me with a Pentronix powered crab and copper plug wires. It had previously run, and did run fine for me for two more years until one day it died. Two Pentronix replacement units later ($$$$), including professionally set-up/rebuilt crab assemblies, the units were still being damaged or destroyed by undetermined causes. The Pentronix tech dept could not help. Despite electric system testing, trying several new coils and alternators, and a lot of work and advice by/from Bubba, we could never find the cause. So I changed to a stock points crab by Charlie NY and have had no further problems. In all of this affair, I give Bubba and Charlie NY my highest regards for their knowledge and services. They remain an outstanding resource to our community.