First, I'd put the action in either a mill or a carefully set up drill press and open the rear hole to a 1/4-28 tpi so it matched the front. A 4mm screw should measure around .160" and the tap drill for a 1/4-28 is a .213" so there's plenty of room to get into virgin material.
Just use a good quality drill and cutting oil and have no fear.
Next. I'd make pillars out of SS, but to each his own.
Scuff the hell out of that stock's inlet to get rid of the gel coat, resin isn't going to stick too well to that for a number of reasons, most importantly its probably still contaminated with mold release from when it was made.
Bed all in one effort. Not one single reason to install pillars and then go back and skin bed over the top. Just more work for yourself and easier to goof up. Consolidate the steps.
Here's a link on a post I wrote in another forum.
Hope it helps. My screen name is "Longrifles" on that site.
Epoxy Bedding - The Firearms Forum.Com
If I can get my photobucket account to work, I'll post up some pics of a finished job.