Update May 4th. The back has safely been removed and image of the movement and internal case back added.

A rare opportunity to buy a vintage watch with the K2071 29 jewel automatic movement, regarded as one of the finest ever made. 18 carat gold case, the 0,750 mark in case back is the modern notation for this, see image.

Only about 800 watches with this movement are thought to ever been produced by Audemars Piguet. 
Movement number has been dated at AP as 1963. The case is 1953 as AP provenance shows the third movement.

The movement's diameter is 29 mm and it is 6.3 mm in height (from previous owner's spec). The beat rate is 18,000 bph.
Case diameter not including crown 35 mm, lug to lug 41 mm.
 
See Google AI summary below.

In original AP branded box. Alligator AP branded strap. Clasp has hallmarks and AP logo.

Good cosmetic condition for age. Expected light wear on case. A 5 mm crack in Plexiglass just above the three. The correct third party replacement size readily available cheaply.
Serviced by professional watchmaker in 2022, itemised service receipt included (not shown) and timing test chart, shown. AP sourced provenance included.

All images and video by seller of this sale. 

Please note the case images are macros and emphasise wear more so than to the wearer's eye. The video gives a better indication of case wear to the unaided eye.

Next day tracked in UK. Expedited FedEx or UPS as buyer prefers overseas, seller will arrange not under the eBay programme which can be more expensive.

Note that import fees such as local tax and/or duties will be payable for an overseas order including for the EU as the UK no longer a member. Please check these before bidding.

Google AI summary of the K2071 caliber:
+3
1961 AUDEMARS PIGUET REF. 3123BA RETAILED BY TURLER K2071 ...
The K2071 caliber is a rare, high-quality automatic watch movement made by Jaeger-LeCoultre exclusively for Audemars Piguet in the late 1950s and 1960s, designed to rival top-tier movements like those from Patek Philippe, featuring an 18k gold rotor, 29 jewels, and used in sought-after vintage AP dress watches, often retailed by stores like Türler. 
Key Characteristics:
  • Manufacturer: Jaeger-LeCoultre (JLC).
  • Usage: Primarily by Audemars Piguet (AP) in vintage timepieces.
  • Type: Self-winding (automatic).
  • Jewels: 29.Seller added: Ruby rollers.
  • Rotor: 18k gold weighted rotor.
  • Significance: Considered one of the best automatic movements of its era, competing with high-end Pateks.
  • Rarity: Produced in limited quantities, making it a collector's item. 
Associated Watches:
  • Often found in Audemars Piguet dress watches, such as the reference 3123BA, which were sometimes oversized for the period (around 36mm) and retailed by prestigious jewelers like Türler.