Yes, I understand that the edges of the granite would need to be done. But I think that is a relatively minor issue. From what I've googled, it seems that the cutout for a drop-in sink is usually larger than for an undermount sink, so it is/may not be possible to put in an undermount sink if you already have a drop-in sink. I'm trying to figure out if/how I can figure out how big my cutout is in the granite for the drop-in sink without removing the sink. Then I might be able to figure out whether the cutout is too big for my new sink. The other thought I had was if the counter is already in place, how do you get the undermount sink in place? It would have to go through the cabinet, right? My cabinets have a wood piece (?frame) running between the double doors, so I'm pretty sure the sink wouldn't fit in that way. I think I'm answering my own question, but I'm hoping that there is a way that's not too complicated to accomplish this.

Not advised to create a ledge. You physically can, but now you depend on silicon to keep things water tight. If you keep a zero reveal or an overhang, then water is less likely to accumulate on the sink flange (Which is used to create the ledge). The silicone then can stay intact longer, and not be needed as the primary water guard. Often the biggest problem we see with ledge sinks is with the installation. Some issues we have been told is with accessories not fitting. However, this is easily avoidable with two best practices: 1. The fabricator should always follow the template 2. Once the hole is cut for the sink, dry fit the accessories to ensure smooth sailing from the client. If you like ledge sinks then check this new release: Kraus Kore

You need to make a very accurate measurement from the bottom of the top to the top of the recess cabinet rail. Is it 8 1/2" or not? If so, an 8" deep sink will fit by 1/2". The other dimensions become irrelevant. If your engineered stone is 2cm with a 2cm edge build up, the bottom of the stone has now moved up 2cm which is a strong 3/4". Now you've got 8 1/2" + 3/4" = 9 1/4" which will accommodate most sinks. On a remodel, your cabinets may need to be shimmed on the top to get to level anyway, but I'd pick up the 1/16" + needed to get a Kohler 3821 into that top anyway. Make sure the sink you pick doesn't have a centered drain please; you want your disposal to clear. I strongly recommend a large single bowl sink.

I doubt your cutout is going to allow you to do so. It's going to look very strange if it's possible at all.