Don't really know as I don't know the thickness of the pintel. But I used 4.5" bolts for my set up, which was the 5T jaw
5/8", the receiver plate 3/8, the EE backing plate 3/8. 4" would have done it as well. If you are using a backing plate
(which you should), then your bolts would be similar in length, I would say 4" would cover it.
Better to measure everything out, and better to have a little room to work with on the bolts. You don't want them too short or just enough for the nut.