Drop-in resolution
Seiko 7S26 vs Miyota 8200: do they swap?
Whether the Seiko 7S26 and Miyota 8200 share a case, and what changes if you move between them.
Different footprints. The Seiko 7S26 is 27.40 mm x 4.90 mm and the Miyota 8200 is 26.00 mm x 5.67 mm, so they do not share a case. This is a choice between platforms, not a swap.
The Seiko 7S26 is the long-running Seiko workhorse behind the SKX and Seiko 5, day-date, non-hacking. The Miyota 8200 is the no-date base of the 8200 family, in clean-dial entry automatics.
They differ in diameter (27.40 mm vs 26.00 mm), height (4.90 mm vs 5.67 mm), calendar layout (centre seconds, day and date at 3 vs centre seconds, no date), winding behaviour. The predecessor of the NH36 at 27.40 mm x 4.90 mm, without hand-winding or hacking. It shares the 27.40 mm case fit of the NH3x family, so an NH36 is the standard upgrade donor into a 7S26 case.
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.