Here's a post I wrote a few years ago on RG...
With all the talk of MBW's lately, I thought it would be good to make a comparison between the MBW 1665 and the MBW 5512.
Through some persistance and nice RG members, I managed to get my hands on these 2 models. The 1665 is modded and the 5512 is stock.
Here you can see the difference in case thickness as well as bezel thickness. These bezels take genuine inserts without any modifications. Also, the crystals are both MBW originals.
These bezel assemblies are 3 pieces, the same as the genuines. They have a crystal retainer, a friction washer, and the bezel. Notice how the 1665 crystal retainer is more substantial and stepped up unlike the 5512 retainer. This is to accommodate the fatter Sea-Dweller bezel.
With the case backs removed, the 1665 has the o-ring groove built into the mid case, but the 5512 has the o-ring groove built into the case back. The 5512 is on the left, with the 1665 on the right.
My 5512 is engraved "ORIG POLEX DESIGN" and "5512" with serial number L342469. It is similar to MBW's 5513 and 1680 case. The 1665 is engraved "REGISTERED DESIGN" and "1665" with serial number 5790134.
Ubiquitous did an excellent write-up on the old style MBW 1680 and 1665 on RWG. That information can be found here:
http://www.rwgforum.com/topic/107-how-to-identify-a-vintage-mbw-rolex/
Hopefully this thread shed some light on the differences between the 2 models, as well as show off the superior bezel assembly, which is unlike any other rep available right now.
The original thread is here...
http://www.repgeek.com/showthread.php?t=92877&highlight=1665