You are misusing the minlen attribute (minlen | Graphviz). Minlen should be an integer that expresses the number of ranks (not inches or pixels) between tail & head for a specific edge.
The result is that dot assigns 20703 ranks to the graph. This causes network simplex to run for as long as it does.
By removing all the minlen references, we get 1748 ranks.
And dot will complete in <3 minutes. Yea!
If you are not satisfied with the result without minlen, we can probably help.
p.s. Cool graph
p.p.s. I was in college in 1969.