In my 47-54 Assembly Manual I find no reference to carriage bolts being used. It only says they are furnished by the Engine Plant, tighten to 55-75 ft lbs and bend the lock ear to lock the bolt. That being said it would seen to be a hex head bolt as there would not be a requirement to lock a carriage bolt ad they are used in a recess. 55-75 ft lbs would require a 1/2" grade 5 bolt if I remember my Eng'r studies but I doubt they are that large. These are the bolts from the engine to the cross-member that pass through the engine mount. Can you clarify exactly which bolts your concerned with?
