Drop-in resolution
Miyota 9015 vs Seiko 4R35: do they swap?
Whether the Miyota 9015 and Seiko 4R35 share a case, and what changes if you move between them.
Different footprints. The Miyota 9015 is 26.00 mm x 3.90 mm and the Seiko 4R35 is 27.40 mm x 5.32 mm, so they do not share a case. This is a choice between platforms, not a swap.
The Miyota 9015 is the slim premium Japanese automatic, a lower-cost slim alternative to the 2892 platform. The Seiko 4R35 is the branded Seiko date automatic behind many Presage and Prospex models.
They differ in diameter (26.00 mm vs 27.40 mm), height (3.90 mm vs 5.32 mm), beat rate (28,800 A/h (4 Hz) vs 21,600 A/h (3 Hz)), winding behaviour. A slim 3.90 mm movement at 26.00 mm diameter that hacks and hand-winds. It shares its dial-foot pattern with the 9039, so the two interchange within a dial built for the 90 series.
Matching diameter and height is necessary but not sufficient. A donor is only a true drop-in when the dial-foot positions, hand-hole sizes, stem length and calendar layout also match. Two movements can share a case and still need a new dial, re-broached hands or a cut-to-length stem.