I've been doing a little work on the blue Prince Date Chrono that Chiman12 was kind enough to sell me and I'm liking the results. Most of these are built on rep A7750 Daytona cases and one of the glaring differences is the Prince Date Chronos have lug holes. The pictures I've seen indicate the holes are smaller than those in Subs so I used a .040" cobalt bit. All went smoothly until the last hole and the bit snapped flush with the case as it started breaking into the existing inner hole. Crap!!!
I ordered a couple of .040" center cutting solid carbide end mills and was able to "peck" the little chunk of bit out and today finished drilling the last hole, replaced the crown tube with a Yuki tube, and fitted the gen crown. I would have been 100% done instead of almost but I managed to knock off the cyclops somewhere so will need to order one from ofrei. I also took a "gtrey" Scotch-Brite and dulled down the case a bit and used a "purple" pad to brush the tops of the lugs as the Daytona cases have the lug tops polished.
Here's a few pics...