Haven't played with the Gorilla epoxies. But as a rule the longer setting (24 hour cure) epoxies set up harder and are better for bedding.

I use a Dremel burr to stuff up the stock prior and get to raw wood instead of the stock finish. For synthetic stocks rough them up as well with 60 grit sandpaper and wipe with solvent alcohol or acetone before bedding. No coincidence glues come in plastic bottles and many epoxies will peel right off some plastics even when cured.

Also, after you first squeeze the action into the stock use strips of sliced credit cards (I keep all those Junk mail cards the mailman brings) to remove as much excess as possible. And don't forget to fill the holes and gaps in the action with clay or Play-Doh first.