I have heard alot about too much load and was too lean and too much nitro and yadda ,yadda.
How about the engine just has many-many hours on it cause it is at least 30 yrs old. Once the wear point reaches too loose it doesn't take long to beat the egg shape. Regular wear will be at top and bottom of con rod because this is where weight of piston takes a violent change in direction and more so at bottom because of added compression and ignition. I just got an old Webra .91 with the dynamix accelerator pump carb. Of course seller said it was good. Upon examination compression was down , con rod egg shaped, Bearing rough with back and forth play. Ring was stuck ,but 3-N-1 oil freed it up to increase the compression. Compression was still down. My conclusion was this engine was not abused but totaly well used. If you take a car engine with 200,000 miles on it the bearings (bushings)are going to be egg shaped and loose. Now if this was done in first season (being a brand new engine) I'd go with the YADDA -YADDA...........We don't even know if the bottom end has been rebushed in it's lifetime ! Or that there wasn't a flaw or air bubble in the metal on the top end.