No problems fitting. A nice snug fit. Generally, if you do encounter problems fitting the retaining ring it's no biggie to sand down the outer diameter of the crystal slightly.
You can pick up rep 702 crown and tube from Athaya, a member here and also other forums. This can installed by countersinking and re-taping the case as described previously. Good luck with your build.
Well, I went for a Yuki 7206. After some modding it didn't turn out too bad. You'll find the story here:
http://rwg.cc/topic/177949-yuki-7206-bracelet-no-longer-accepts-gen-spec-bars#comment-1450950
My mistake, typing error. Apologies for the confusion. To seat the Athaya tube snugly, I used a 6.3 mm x M3-90 degree countersinker first to create the sloping 45 degree angle. Then a ca.3.2 mm drill bit to widen the hole ever so slightly to a depth of ca.0.3 mm. This creates a small step and angled sides for the tube to sit in. I then cleaned, and extended, the remaining case thread carefully using a M3 x 0.35 tap.