I ran the numbers, and with 4.10s, a 27.5" outer tire diameter, and the 1:1 fourth gear ratio of the 5R55S transmission, at 140 MPH you're looking at just over 7000 RPM, not taking into account and torque converter slippage. Based on what you want, I'd either get a slightly oversized tire, say 30" diameter, or build the engine to exceed 7500 RPM. A 30" tire drops you down to 6400 RPM. That's the safer route. Yes, the numbers for the rotating assembly sound correct. Different factors can have a large affect on the aluminum block's strength. Most people with agree that the factory block will support around 650 horsepower, but Blowby Racing sells a billet crankshaft girdle that increases that limit to around 1000 horsepower. While I have no experience using girdles on the modular 3V, I can say they work great on older Chevy engines. The theory is sound, but there's an inherrant risk to everything. Another thing to consider is whether or not you NEED the extra couple of cubic inches you'd gain by boring the cylinders, which thins and weakens the cylinder walls. Or, you can avoid the entire situation by shopping around for a built short block, either iron or aluminum, that will give you the strength that you're looking for.