Location, location,location. Yes. I said screw it up. - 2002 J. Broz    

I like to use 6/32 long screws to locate the halves.
These also hold the mold togther to limit flash.
The screws and nails remove easily after curing.
Sometimes resin gets in the threads but a thread die, clears them out.
If your silicone flows higher than the screw head,
you may have to cut down to grab it with long nose pliers.
You may also notice the primer barrier to seperate the second pour from the first.