I just changed the crank position sensor on my '99 Ram 5.2...
The hex part of the 2 fastening bolts is 13mm.
What will save you aggravation, is knowing that they also have a 1/4" allen socket in the center of the bolt head. Once you break them loose (I used a 1/4" drive rachet), a regular allen wrench gives you a nice clean access to 'em. There's not enough room for the socket to back them out (at least there was stupid tight clearances ). If they're not too tight, you could probably start out with the allen wrench.
The bolts & sensor are on the passenger side bellhousing behind the cylinder head by the trans dipstick tube.

Rick