B&S Engine Age

[Yeoman627]

I am trying to deterine the age of the B&S 19 cubic inch engine I am rebuilding. Normally the date of manufacture could be found stamped on the flywheel cover (model/type/code). However, when I obtained this engine the flywheel cover was missing. Are there any 'tell-tale' characteristics I could look for to help me determine the age of the engine ? For example, I noticed that there was no hole in the crankcase for the 'plunger' of the old 'internal breaker' type ignition systems. Most engines I've restored from the 70s that were setup with Magnatron ignition systems had a plug where the plunger would have gone. At some point, B&S must have either changed the casting or eliminated some drilling when Magnatron ignitions replace conventional points. Any help would be greatly appreciated. Regards, Tom Kelly