I have my skid plate out right now, and just checked the baggy of bolts. There are 5 bolts, and they are all 3/8-16 and 1" long. They have some really beefy washers, 1/8" thick - and the washers are captured on the bolts so they can't be removed. They have a grade marking "EL" and 3 hash marks, like the attached picture. Not sure this matters, grade 8 would likely be fine.
If you had asked last week I could have gotten you the trans crossmember too. I just put it back in a couple days ago. Let's see if somebody else can help out before I unbolt it again, please.