I have 3 "E58 motors, all out of 79 300's. Two I had sonic checked and all had thick walls ( around .200"). The E58 motor had a bunch of special parts in it. The block should be stamped 360HP with serial #. Fifth digit of the VIN should be "L" for E58 engine car. Body code plate should have "E58" stamped on it. E 58 engines also came with a windage tray ( same as early HP 340's and 360's), specially selected ( what ever that means )cast iron crank, Larger cast iron exhaust manifolds, "360 Premium engine" sticker on the valve covers. Not sure on the last item on California package cars though. Engine ID is located just below left cylinder head. Example: 9W 360HP 6345. Translates to: 9=1979, W= Windsor plant, 360HP = displacement, 6345 = date code ( Dec. 11, 1979) Above info came from printed Chrysler data. Got a problem, take it up with them.