The current center bolts are 3/8-24 hex head with no lock washer under the head. The non-threaded shoulder of one extends below the area needed for the nut to thread onto. Both center bolts are sitting loose in the holes - not nutted.
< PIC >I figure that a previous owner discovered that he couldn't insert 7/16" carriage bolts through the front plate after he had assembled the engine. Don't know why he chose the long-shouldered bolt. Also don't know why he didn't secure the nuts better. It's never had nuts on the center bolts since I have owned the truck (12yrs). I believe that one of the bolts on the side motor mounts was missing when I bought the truck. The weight of the motor was all that kept it in place!
