There is extra meat where it counts, I posted pics. The iron is clearly harder, try grinding one block then the other. Cylinder walls though thinner on average are very much more consistant and the bad spots are not as bad as the older stuff and remember a chain is only as strong as it's weekest link, if you have one thin spot in a block with 1/2 inch thick bores it can wreck the entire thing. 9 out of 10 magnum heads are cracked... SO WHAT? How many does it cause a problem on? I never seen one and have worked with 100s of magnum powered trucks, if it was an issue you would see steam coming out the exhaust on most 92-03 dodge trucks. No stock head LA or Magnum makes enough power to bust any block (unless you get one with a thin spot of course) so who cares. Add on top of all that the 45 years of poor coolant maintnance corroding them up. I am not saying a LA block is a ticking time bomb but if you are really pushing the limits the mag block is stronger, how much I don't know but to deny it is stronger is foolish or in-experienced. As fer a 340 block, so what if you got .020 more clearance on 1/4 of the intake valve, .040 bore barely makes a measurable flow increase if any. Sure I would love to get a 4.25 siamese bore but for most heads out there it won't make any HP difference only more TQ but so will a dirt cheap roller cam. You can sell a 340 block buy a magnum, regrind the cam core bore and square deck it with the money.