If you are gonna do a stroker why not put the 400 crank in the 350 and get 383 inches. You are now talking about equal machining dollars because the block will have to be machined to accept any crank. that is a free 48 cubes, and a much better combo. Having a good 350, and going backwards to a smaller displacement engine, does not sound logical. 350 blocks are a dime a dozen, and 5.7" rods can just about be found at the local grocery store. (personally I would use a 6.00" rod, the extra piston duration has big advantages, and relieves some cylinder side loads.) Unless I was racing a specific class that limited cubic inches to less than 350, this would not be the way to go for me.