olddog,
I AM going to tell you that they're internally balanced, as all our crates are. Sorry I didn't think to mention it.
blykins has it exactly right, the block doesn't affect the balance. There IS room in our blocks for stroke: 4.00 in this 9.5, 3.47 in our 8.2. In the iron version we use a 4.250 for 460 inches. This room comes from using the 351
oil pump and distributor location in our casting.
You're right about splitting the OE, they like to go vertically from the main saddle to the cam tunnel on the front or rear bulkheads. Sometimes further back. Our bulkheads are nearly twice as thick, so the iron weighs more than OE or some other aftermarket blocks. That's how it lives at 2800 HP.
The aluminium version has webs in the valley and stiffening ribs on the rear bulkhead around the crank journal / rear main. They are visible in one of the thumbnails I posted on the Advertisers Forum.
Well it won't rust but I hope I'm not asked to polish them! Actually, you can't believe how beautiful the casting is up close-very fine texture 357 T6 not coarse at all.
I'm contemplating a swap into my ERA when production gets going. To replace my uh-Side Oiler...