Are all 340 blocks the same?

Totally bullshit. Yes. Any block should be sonic tested at the level you want to reach regardless of displacement. The issue is not the lower end, but the cylinder walls. If you go with a 4" stoke it doesn't matter. Bearing speed will not be a concern with what you're doing.
OK, so the mains are not the problem area. I'm not using 4" stoke. I'll likely be going with a brand new forged crank with 3.58" stroke. The plan is to not build a small block that runs like a big block. I don't need or want a big fat torque curve or low end torque with this engine. I'm not going crazy with huge heads either, going to be very carefully looking for someone who can port Eddy RPMs or something similar to deliver somewhere between 280 and 300 cfm without exceeding .650" lift and hopefully not kill the low and mid lift flow. It is going to be high compression around 13 to 1 and run race fuel. I'm planning on running my car in The Gear Jammers races which is all manual trans. Going to a four speed and what ever rear gears will put it through the traps in the 1/8 mile at the top of 4th gear. I want to build it to make maximum power between 5000-7500 rpm and completely ignore the numbers below 5000. The cam will be custom ground to match the heads and intake as best as possible and it also all has to fit under the flat hood with an air cleaner. Its about working within constraints instead of just going crazy with huge parts. If I had the time and money I would build a stock eliminator car but I don't so gear jammers looks like a good alternative.