The 305 and 350 cranks are the same casting. But, the 305 is milled through the counterweights. The only way to use one in a 350 is to have your machinest add mallory metal. Why would you do that? Much more expensive than buying a good 350 core. Your machinest will most likely have one or two on hand.

And I agree about the 305 heads.

With gas prices going up a 305 does not look like a bad deal.