Stroking shouldn't be discussed on an open forum..... 
I agree with the earlier posts though that there is more stress on piston skirts as they go farther down in their bores and also that the piston speed is increased since it travels more distance with every revolution. Seems to me that the trade off with a longer stroke is less RPM potential.
As far as the six cylinders, not sure if their cylinders are a touch longer to provide additional piston skirt support but even if they are not, the stress placed on a six cylinder piston is dramatically less than a 450 HP stroked engine.
I can imagine that back when the 340 was designed, they may have considered things like:
1) keeping displacement at 340 versus 400 plus for some racing regulation or internal company policy on displacement limits.
2) maybe materials back then didn't hold up as well to the increased stressses of a high performance engine with a longer stroke. Materials are vastly better in strength and lightness today.
3) maybe they didn't want to outperform big blocks. They had big money tied up in the research and production of big blocks at the time. Who would pay extra for the heavier weaker big block motor?
4) maybe they were concerned about durability and longevity of the motors. Hurts business to sell motors that don't hold up as well as the competition
5) maybe they saw insurance issues on the horizon and wanted to find a balance between customer demand for performance and insurance crackdowns which hurt sales
6) probably more work and expense in producing a stroked version with beefed up components and they may have wanted to keep costs down so they could sell more. As awesome as the hemi was, almost no one could afford it so in a sense, it was over engeneered from a production/sales point of view.
Okay, now I can say I officially over analyzed the matter!
