Did my initial design in Google Sketchup (love this program!)
Materials sized and cut, ready for assembly. Bottom plate is 3/8, as well as the top die. 5/8 inch bolts. Springs I bought from Ace Hardware for .60 a piece.
I drilled the bottom plate with a 19/32 drill bit (1/32 under 5/8), then ground a taper on the ends of the 5/8 bolts.
With the taper on the ends I tapped the bolts into place to enable me to make sure they were parallel and 90 degrees to the bottom plate.