All those Blocks are surprisingly very strong I sure wasn't making much power back in the late 1960's as a teenager but I pushed them really hard never Damaged even the early blocks 1954 to 1960 223's, those had a poor oiling system. On the 223 the two Main Weak Points are the Stock Rod and Piston The Cylinder Walls are very Thick too it was not uncommon for them to get bored out .060 to .120 during the many rebuilds during their lifetimes. The 1961 to 1964 223 Block's had an improved Oiling system, same as the 1961 to 1965 262 Blocks which are even stronger yet with an extra 20 Pounds of extra Ribs and Main Webs Cast into them. At 6000 or more RPM the Bonneville Race 262 did not break any of the Main Webbing or damage the Crankshaft. It looks like the Cylinder Walls were the weakest point in his engine and I still don't know how far he had bored it out. He had said that he was going to use the block Grout in it up to 2 inch below the deck, but then I guess he decided not to after some comments by others that had used that product that it would cause movement of the Cylinder walls around since the Block had all ready been completely machinated with the bore and finish honing to the size. He had also built a Block Gridle for his first engine combo but later on when he was lowering the front of the truck more for better Air flow over it he took it out. These blocks have very Deep Side Skirts like on the old Y Block and FE V8's, I would think that some custom Main Caps could be made where you could then Cross Bolt the Mains to the side skirts like they did on all the 427 FE Blocks, then a simple block Gridle could also be added to so that Bottom end could handle lots more than the power then you could probably make. I would say with the good BB Chev Rods and a good set of Forged Pistons north of 600 HP should be doable. No luck yet in finding a 262 Six I did locate a 1961 or 1962 223 Engine Core, its one of those that Ran sorta when it was pulled out with maybe has a bad Head Gasket or???? It's all ready been Bored out to .030 over with a .010, .010 Crankshaft according to the Stamped Metal Rebuilder's Tag.