http://www.stovebolt.com/techtips/engines/motor_mount_front/index.html

You do not want it to touch, you will get a bad vibration transfer.

The shop manual calls for clearance.

Bottom right
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0613.htm

I don't believe there is a torque value. Just snug, my original bolts had a provision for a Cotter pin.