[Ron Ramirez]

I answered this question in post #4 above:

There was a production change in both 37-620 and 37-630 which eliminated some trimmers. Philco issued a Service Bulletin which covered both models.

Perhaps you can get this from Chuck?

You have a 37-630 Code 126. The schematic and parts layout for this version does not match the schematic/parts layout in Rider's. See if Chuck has it.