Drop-in resolution
ETA 2892-A2 vs Seiko 6R35: do they swap?
Whether the ETA 2892-A2 and Seiko 6R35 share a case, and what changes if you move between them.
Different footprints. The ETA 2892-A2 is 25.60 mm x 3.60 mm and the Seiko 6R35 is 27.40 mm x 5.25 mm, so they do not share a case. This is a choice between platforms, not a swap.
The ETA 2892-A2 is the slim upmarket automatic, base for many chronograph modules and higher-end pieces. The Seiko 6R35 is the long-reserve Seiko date automatic, in higher-end Prospex and Presage models.
They differ in diameter (25.60 mm vs 27.40 mm), height (3.60 mm vs 5.25 mm), beat rate (28,800 A/h (4 Hz) vs 21,600 A/h (3 Hz)), winding behaviour. Same 25.60 mm diameter as the 2824-2 but only 3.60 mm tall, a full millimetre thinner. It is a slimmer platform, not a drop-in for a 2824 case, because the reduced height changes hand heights and case seating.
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.