Why do such a mod? Well, My friend 7 gor had a 7549-7010 with a dead movement (probably due to bad coil) and he decided to convert it to become a day-date auto tuna. From the case design, we can speculate that the perhaps the original plan is to make one with a automatic movement. However, since the 1979s was the period of the Quartz watches, naturally, the 7549-7010 was fitted with a quartz movement.
The 7549-7010 has several compatible parts (with the 6309-7040/7290) , which are : bezel insert, caseback, crown (except the stem), gaskets related to the above are also compatible (bezel gasket, crown gasket, caseback gasket). Crystal and crystal gasket are NOT compatible.