Drop-in resolution
Seiko 4R36 vs Seiko NH34 (TMI NH34A): do they swap?
Whether the Seiko 4R36 and Seiko NH34 (TMI NH34A) share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Seiko 4R36 (27.40 mm x 5.32 mm) and Seiko NH34 (TMI NH34A) (27.40 mm x 5.32 mm) are near in size but differ in height, dial feet or layout, so moving between them means a new dial, hands and often a case adjustment.
The Seiko 4R36 is the branded day-date Seiko automatic, the retail version of the NH36. The Seiko NH34 (TMI NH34A) is the affordable modding GMT automatic, adding a caller-GMT hand to the NH35 base.
They differ in calendar layout (centre seconds, day and date at 3 vs centre seconds, GMT 24h hand, date at 3). The branded day-date Seiko at 27.40 mm x 5.32 mm that the NH36 copies. It shares the NH3x footprint and stem, so it drops into an NH36 case with a matching day-date dial.
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.