Those bolts are threaded 3/8"-16, so replacing them with a hex head capscrew is easy. I don't recall how long they are, but you can take one of the old ones out and measure the length under the head to get it. The replacements were available off-the-shelf, as I recall.
The lower bolts, as I recall, are threaded 7/16"-14, somewhere in the neighbourhood of two to two and a half inches long. Again, replace with hex head capscrews, which you can get easily anywhere.
5-90