Not taking sides because the ad was obviously mis-stated. but i will say one thing, what you have is a 3970010 /350 blk. which is a Hi-Nickel blk, the best blk that GM ever cast and probably a 4 bolt main blk. It's worth (2) 400 blks to most anyone building a 350/383" motor due too the tougher blk and the thicker cylinder walls and will run cooler than any 406" engine ever will. I just finished a 383" for a customer with a 3970010 blk last week, which will produce around 575 HP and live running alcohol injection.
JMO
Zip.