"What diamater bolts did you use to mount the Lee Classic Cast press?"
Take a ruler and measure the holes, probably 3/8".
If your bench top is thick, get a length of "All Thread", threaded rod, and some washers and nuts from your local home center big box store instead of using bolts. Just cut the rod to the lengths you need to secure the press.
You will find it easier to install if you bore your bench holes a tad larger than the rod diameter, like for 3/8" rod use a 7/16" bit, etc.