The NH part may fit... but probably not. The critical parts like the bill hooks ARE the same... but once you deviate out further in the larger parts the design is different.
What you can do is go to NH online parts and look up what you need. Then take that number and plug it into Messicks parts online and see if it supercedes to something else. If it does, keep following it and see if it's available or what it fits.
A NH dealer can also plug the part # into PAL and see what else it fits besides that baler.
They may also be able to still do a parts broadcast requesting any other dealers with NOS on the shelf to fill your part order if they wish. They used to have that feature anyhow... unless that's been done away with.
As far as the shattered part... if you can find the crumbs sometimes Humpty can be put back together. You just need the critical stuff to get the angle right. Cast usually breaks pretty clean without distorting so as long as you can jig it the way it needs to be set and hold it... someone with cast experience can probably weld it.
I don't know of any wreckers that would bother keeping a baler like that in the yard. You could try Fawcett tractor. They might also steer you to someone who does wreck that stuff.
I find that every year or so I see a 532 or 542 in the junk sale. I've yet to drag one home... The last one was kinda nice and went for over 650 which I thought was a bit dear for a parts haul... that I'd have had to float home because it had junk tires.