Drop-in resolution
ETA 2892-A2 vs ETA 2804-2: do they swap?
Whether the ETA 2892-A2 and ETA 2804-2 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The ETA 2892-A2 (25.60 mm x 3.60 mm) and ETA 2804-2 (25.60 mm x 3.35 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 ETA 2892-A2 is the slim upmarket automatic, base for many chronograph modules and higher-end pieces. The ETA 2804-2 is the hand-wound date member of the 2800 family, the manual sibling of the 2824-2.
They differ in height (3.60 mm vs 3.35 mm), 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.