67' 318 crank in a 69' 340

nm9stheham said

Not sure what the thought is... if lighter pistons are put in, it needs to be rebalanced.

Are you thinking that the external balance weights can be done away with? I.e., go to neutral balance damper and flywheel/flexplate? For the cast 340, there is some chance. 70aarcuda has reported coming pretty close to neutral balance with the cast 360 cranks with the very lightest pistons and rods, and it would be easier to reach that point with the cast 340 since the external imbalance weight is a lot less.

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I thought the OP wanted to use a 318 crank which has a lighter balance stock. If a guy was real lucky, there just might be a piston that would weigh the right amount so no balancing would be required. Magnum pistons come to mind as something to look at. Magnum rods are also lighter. There are a lot of ways to skin a cat: Hbeam rods are lighter, some sbc parts might make a combo, but that would be getting into territory for veteran engine builders that have seen a zillion parts. For instance I currently have a 5.9 cast crank, a set of sbc h beam 6.2 long 2.00 rod bearing rods. Find a sbc piston with the right deck height and enough meat for valve notches, and with luck I just might come up with a little stroker kit with a pretty light bob weight!