Any ideas on this 340 block ?

Cledus said
How well does molasses work and how long do you leave it in it. I have used muratic acid on cranks in a bucket 10 minutes and done

Check out "project farm"s you tube video on rusr removal. Tests vinegar, molasses, evaporust, and muriatic acid.
Basically, molasses works excellent, it's dirt cheap, it just takes lots of time, and stinks. Does not harm parent metal at all.