crankshaft help

You are right: 360's were externally balanced, the others were internally balanced. The 360 has a longer stroke than the 273, 318, 340 and the mains on a 360 are bigger than the others, too. If you want to make a stroker of the 340, you could get the mains on a 360 crank turned down to 340 size and use it. Otherwise, stroke and main size is the same on the other small blocks. The cranks were forged on some of the small blocks early on. 273's and 340's I know were, but not sure of the years. If you're keeping it below 500 HP, a cast crank will be good.