I notice that a lot of JDM clubs come with non-vented brass tip weights. Any thoughts on how they keep the heads from floating on installation?

the easiest way to prevent the shaft from sliding due to the fact u are creating a vacuum with a tip weight is to install tip weight into the head and then place the shaft into it....if u are still getting sliding...u are using too much epoxy....i would put a thin coat on the hosel interior walls and a very light coating on the shaft and drop the tip weight into the hosel and then slide the shaft in.

Another way to alleviate problem is mix centering beads into your epoxy and turn the head as you insert the shaft. The beads not only insure that the shaft will be centered, they also provide gaps for the air to escape.

Yep, shafting beads is the way to go. I use them with every build