Fordboy;
Whatever it is, it's not trivial. I do have an el cheapo attachment for my cell phone that is a video camera fiber optic probe so I'll take a look in the cylinders to see if the engine ingested a foreign object, dropped a valve, etc. My guess, though, is that the noise is associated with the bottom end. We'll see. I'm committed to a car show on Saturday so I'll take it to town tomorrow and just tow it onto the field. I'll need some time to pull the engine/transaxle to do a teardown. I designed my chassis so I could remove a few tubes and then remove the engine & transaxle as an assembly so that makes it a bit easier.
Regards, Neil Tucson, AZ