Thanks Rustynutz, this is what I am talking about. For one the appearance of a "restored" trucks should at least appear that way, on a second note, these holes are NOT just 3/8 holes, but an odd size of 13/32, therefore by installing just the 3/8 bolts, they inevetibly would work loose as the frame twists, and eventually egge shape all the holes. The rivets are installed hot, and hammered to swell in the hole filling the little bit of gap there is for movement. I'm sorry, but I have been a mechanic for too long and have seen this type of thing happen. Remember, this is a restoration, not just bolting peices together to make something work, there is a difference.
Thanks for all who replied.