Gruen Doctor watch 1930s with chronometer grade movement

This is an "unusal" vintage 1930s Gruen Doctor watch. What is unique about this is that the movement is Chronometer grade Timed 6 positions Rolex cailber 300 marking movement. Normally, there are many Rolex Prince doctor’s watch using Gruen movement as both Rolex and Gruen (and Aplina Gruen) movements are being produced by the same manufacturer Aegler in Bienne using caliber 877 and they are basically interchangeable.

Example of Gruen movement being used in Rolex Prince watch

Gruen is sold mainly in the US while Rolex vintage Prince watches were sold more in the commonwealth countries. Rolex sold this watch as the Prince in Europe and throughout the British Empire, marketing it to “men of distinction,” while Gruen sold it in the U.S. to the “man who requires the exact time in seconds.” Gruen sold its shares in Aegler in 1934, which effectively ended the production of the Techni-Quadron. With Gruen out of the way, Rolex was allowed to sell the Prince in the United States, which it did from the 1940s to the 195

Rolex Prince tends to play around with the outer case design (Straight case, Railway, Brancard case) while Gruen focuses on case design as  well as having filigree engraving on the case.

Some history : After the stock market crash of 1929, Aegler purchased 6960 shares of Rolex, and Hermann Aegler was granted a position on the board. This would establish a long and fruitful partnership, which still continues to this day: in the 1930s, Hermann Aegler would sell his shares of Rolex back to Hans Wilsdorf, the founder of Rolex, and Rolex would eventually buy Aegler’s factory in 2004.

Guen cased Doctor's watch but it is fitted with a Rolex cal 300 movement

I am contemplating in doing a project to rectify the mis-matched movement vs case. I have already a set of old Rolex steel outer and inner case. Just needed a Rolex dial.... a project maybe...