"So, the Cartel 1680 isn't even worth looking at for less than $150? What are the issues?"
They are hit or miss in specs and overall quality. Most are made for Eta 28xx or Asian '21 jewel' movements, not rolex. Some are oem spec as far as case neck etc and will accept ST/Clark oem spec bezels, crystals etc but some are out of spec. Most have the correct case tube threads but the cases may not be machined for oem gaskets between the case tube and case.
"Yuki said 1680 case is discontinued, though Ruby has them for $650 (ouch). If one were willing to drop $650 on the Ruby, what's needed to get a 2846 working? Spacer? And will an overlay solve the ETA datewheel location issue?"
Iirc a Yuki 1680 was that much or more up until they were discontinued. Their 5512/13 cases were $600 each in mid 2014 with random serial numbers, special s/n were more. They discounted $50 each on two cases when I got a 5512 and a 5513 at the same time so it made them $550 each. The cases were top quality.
An Eta 2846 is smaller in diameter than a rolex 15xx so any case made for a rolex movement will need a special spacer. DWOs come in different versions so you will need to zero in on one that suits you and track one down. They are a pain imho...hard to index/glue down over the original DW, then you will have to be sure there is enough room between the DWO and dial, next you have to make sure the hands mount far enough away from the dial...if not you will need a taller hour wheel, CP, center sweep pinion, hour wheel etc. And on and on...
A 5512/13 project is much easier.
"I like the idea of using an MBW, but they're hard to come by and when they do, the Ruby case is a small jump in $$ more."
True. Since the last batch of MBK watches were over $400, an empty case will probably be that much by now. I posted some info about MBK cases at the top of the rolex section in the stickies.
"The winding crown is too low on the Cartel cases and they are far too thick. They are pretty much all the same case, so 1680 is actually a 5513 and the dial opening is too small, so won’t take the good aftermarket 1680 dials if I remember correctly."
Same with MBK...they are 1680 spec cases with a 5513 spec dial window. They are not overly thick though and the quality is first rate.
Free advice:
Find something inexpensive that you like and buy it now to wear while you go through the long drawn out process of putting a project watch together. It may take a few months...or a year. This is not meant to discourage anyone, it is just a word of advice from someone who has been around the block.
Example...my '1655' project has been on/off for 5+ years.
Why?
Because GMT part$ are expensive and hard to find.
Looks like someone else found this out the hard way, a 1575GMT rolex movement just went for $3600 on eBay:
ROLEX GMT MASTER MOVEMENT Ref. 1570/1575 for GMT MASTER 1675 Explorer II, 1655
VINTAGE MOVEMENT / Fully Serviced / Sold AS IS
eBay item number: 163171371202
Ended:
Aug 06, 2018 , 10:29PM
Winning bid:
US $3,600.00
Shipping:
$50.00 Expedited Shipping