Hello,
so my project is now mostly completed. Lots of things I learn and lots of mistakes I made.
Regarding the eta 2846:
Turns out it's wouldn't normally fit in the raffle 2824 case. Since the stem height of the 2846 is higher than the 2824. However, since I'm not running a date complication. I removed the dial spacer and everything lines up well. If I hadn't modifyed the case, the hands would have hit the crystal. But since I have an acrylic one, it's not a problem.
Also, at the beginning during service I replaced the original mainspring with the one from a 2824. What happened is that the mainspring from the 2824 is too strong and would yield way too high an amplitude (~340 degrees) causing the balance to "overbank", thus throwing off the timekeeping. I had to refit the older mainspring and now everything is fine. This is due to the difference of beat per hours between the two movements.
So to anyone wanting to convert an eta 2824 to a low beat movement by installing an escapment from an ETA 2846, don't forget to also replace the mainspring.
Another major annoyance I had, is the return spring from the keyless mechanism not wanting to stay in place when removing the stem. So I had to refit it 3 times by removing hands and dials, very annoying. Which is also why I feel a bit reticent shortening the stem more. It fits, but I now I could maybe shave half a milimeter more.
As for the timekeeping, I managed to get running fairly well, let's see how the timekeeping will be with real world usage.
Otherwise I'm quite happy very everything. I'm just not so sure about the bracelet, since to me the quality feels quite cheap and rattly. But maybe the originals were also like that. I might install a rubber tropic strap.