If you are asking if a 123 5 cyl engine will fit the 115 chassis, well technically its not impossible. The biggest problem is the oil filter cannister on the 123 engine will hit the steering box so unless you had a filter bypass kit (rare) a 123 engine won't fit a 115 chassis.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!