Sorry, can't help you on the bolts. From what I've observed the correct bolts are not sold anywhere, you'll need to scrounge them off of similar vintage engines (not easy). Be forewarned, there various vendors on ebay and other places that sell "O.E." correct bolts and they have completely different markings. They may be right for some small blocks, some years, but when it comes to the original 70-71 340's I've seen, they are all wrong.

J = September 0 = 1970 = Perfectly acceptable on your December 14, 1970 assembled engine.