RSM2008 - I usually use a combination of Super Glue Gel and the epoxy putty. If I was doing what you'll be doing I would knead up a ball of epoxy putty, then put a decent blob of SG Gel on the frag disk and press the putty down on that, then make an indentation in the top of the putty you just put on the frag disk and put a blob of SG Gel into that. Dry off the bottom of the remaing snail shell (or the bottom of the calcium base of the LPS), then press that onto the blob of glue on the putty, and put it in the tank. Keeping the LPS is a small amount of tank water till the last step is good to keep it from drying out. The putty is great for conforming to the uneven texture of coral bases and rock, but I've never had much success with the putty bonding well by itself. So I use the Super Glue Gel to help with the bonding.
The putty will start to harden in about 5 - 10 minutes, so be aware of that. Both the putty and the SG Gel will further harden and bond underwater.