Looks surprisingly good on the Red Zulu David !

I haven't dismantled anything but I don't think I need to, Ive studied the aftermarket insert side by side with my Monnin, and it looks like a perfect fit.
I took some crude photos, but you get the idea. My Monnin is the one at the bottom with the bracelet. The top-down photo - note that the aftermarket case sits lower because there is no bracelet under it, so it appears a tad smaller, but it isn't!! Oh, and it has a protective plastic disc on it, just in case you wondered what it was.

My conclusion is that..

a. The insert will fit. (my best guess)
b. Highly likely that the metal bezel is the right size, but the grooves that attached the wire to hold onto the case may not be compatible. I have no idea.
c. The case is to be discarded, it's a different profile and has 22mm lugs (not that anyone would want to use an incorrect case anyway). But is worth noting in case anyone tries to fashion a fake or franken Monnin/844. A Monnin has 20mm lugs!! PS. The crown may be a fit, worth hanging onto it just in case as an emergency spare, but I've no idea if it will fit.

Stewart
- Heuerville