Change from TR2 to TR3 Turn Signals

On my 57 TR3 I had the typical layout for all rear lights that later TR3's had. Outside break/tail lamps, inboard turn signals, and center plate light. What was different with mine was that the inboard turn signal lamps were bolted to the body (with a gasket between the body shell and the turn signal base), and not stamped into the body shell. My commission number was TS16100L. I think that puts it as an early 57.

The question that has bugged me over 25 years is two fold: (1) Has any one seen another TR with bolt on turn signals, and (2) does any one know at what commission number was the change made from the TR2 light setup?

Mark