Believe me... If you can do the ETAs, fitting a gen Rolex movement in a case that's designed for a gen movement will be a piece of cake! With the ETA swaps and retrofits, you have a number of things to contend with... Everything from aligning datewheel overlays and making sure dials with missing dial feet are straight... Installing the dial with enough clearance for the datewheel so it doesn't rub or stick... Ensuring that the right ETA is installed so the stem lines up center in the tube... Making sure that the case clamps aren't applying too much pressure to the movement, but rather just enough to keep the movement from shifting around when the stem is pulled out to set the time, etc. There are a lot of variables to check and double check, and I've spent many an hour assembling, disassembling, adjusting and repeating many times over to get things just right...
Whereas a Rolex 1570 movement going into a case meant for a 1570 is basically plug and play Almost takes the fun out of it all... Almost I'd definitely say that I learned more doing the ETA stuff!
Thanks, buddy It's definitely coming along...