Sean brought me a 1600 DP core to tear down and examine. Things didn't go so well....
The first red flag was the JB Weld gooped on the outside of the case. Upon teardown it looks like they "tried" to seal up the big crack but missed, or maybe it spread after gluing. The #1 main was a mess- not only was the dowel loose and the bearing rotating, but it had pounded out the saddle very badly and worn the thrust about an eighth inch! The groove I'm pointing to isn't supposed to be there. The heads weren't much better- someone had cut the seats and faces way too much, the margin was gone on the valves and the seats (and guides) need replacing.
Not fixable, scrap. I think a new case and heads would be a good investment here.