As far as what grade bolt to use for this application is concerned, when there is a failure in this area, it is the crossmember hole which gives out before bolts do.
The entire weight of the front clip rests on this tiny footprint on the crossmember. A good way to tell if your truck was originally subjected to off-road farm work would be to look at the condition of the crossmember under the radiator support.
There is a rubber pad and a shim or two between the radiator support and the crossmember. As the rubber pad gets beaten senseless, there will be slop there which will create a significant amount of hammering, causing damage to the crossmember and wallering out the holes, while the bolts will remain just fine.
