Question concerning bolts for frame

[68jimmy]

I'm getting ready to swap out my 3/4 ton suspension for a 1/2 setup and I will have to remove the crossmember rivets. I'm going to use a 7/16 bolt with a flat and lock washer but was wondering if I should go with grade 5 or 8? And should I consider using the nylock nuts instead or use some red threadlocker?

Thanks, and have a safe and happy thanksgiving!