Drop-in resolution
ETA 2836-2 vs ETA 2834-2: do they swap?
Whether the ETA 2836-2 and ETA 2834-2 share a case, and what changes if you move between them.
Different footprints. The ETA 2836-2 is 25.60 mm x 5.05 mm and the ETA 2834-2 is 29.00 mm x 5.05 mm, so they do not share a case. This is a choice between platforms, not a swap.
The ETA 2836-2 is the day-date sibling of the 2824-2, in dressier and tool watches that show the weekday. The ETA 2834-2 is the panoramic day-date member of the 2800 family, with the weekday at 12.
They differ in diameter (25.60 mm vs 29.00 mm), calendar layout (centre seconds, day and date at 3 vs centre seconds, day at 12 and date at 3). Same 25.60 mm diameter as the 2824-2 but taller at 5.05 mm because of the added day disc. A 2824-2 will not fill a 2836 dial: the day window sits empty.
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.