Spun bearings are all about the clearances.. .002-.0025" will keep them from spinning.. Sorry to hear about your misfortune.
I should have read the post and not just the headline. It sounds like you had a siezure rather than a spun bearing, or more likely had a crud induced failure. 3 hours isn't enough to get a good break in before flogging.. Did you change the original fluid before the fun began???
Either way, I might have gone at least 500 miles before serious flogging began, more really.
You will be able to see crud embedded in your bearings if you have sucked something up that dislodged from inadaquate cleaning of the crank, journals, block cavities, etc. or anywhere really. Hotrod or Car Craft did an article on bearing failurein the past few months. I will try to find your address and send you the issue.