340 parts interchange & performance Q

Didn't the 73 340s drop to 240HP instead of 290HP at stock?? If so, you're looking at doing more than what you plan to reach 300HP. Also, you cannot use a 318 crank in a 340, the main journals are different sizes and these cranks wll not interchange. Otherwise everyone would buy 318 blocks and put 340 cranks in them for an on the cheap build.