Hi been following your story for a while. sounds like you got the brown end of the stick with this tractor having a re built motor!.There are some real honest people out there L.O.L. Hopefully the new crank will be good quality there are a few made in China junk ones out there. Maybe someone here can recommend one at a sensible price. I trust my motor shop guys to supply me with good quality sensible priced ones, when needed.
Yes you do need to change all the bearings, you already got a half a@#ed motor now. the bearings are probably worn if not destroyed. you might have over sized bearings if the cranks already ground, from standard that won't fit the new crank. I would probably check the oil pump real good for wear to. No point in putting crank / bearings, other new parts in if the hearts not gonna outlive the patient. Low oil pressure will kill your new bearings pretty quick. Regards Robert