I have a copy of the Tecumseh service manual for cast iron engines (like the one you have) I'll be glad to email the pdf if you'd pm me your email.
Another member, GT80, also has this manual posted on a website to download. ( I don't have the link nearby, but a search will find it)
I have limited experience with these engines, but I understand that it is NOT uncommon for the solid state ignitions to fail. I think you are on the right track attempting to diagnose the problem first. (rather than throwing parts at the problem)
I believe the only options, if it has failed, is to replace with used parts or convert to a different type of electronic ignition
Good luck
I'm sure there are several members with more experience than I have willing to chip in.
Mark