A new crankshaft is terribly expensive, especially for multiple cylinders. As long as the shaft is straight, the oval areas can be remachined for roundness. Of course the piston rod and/or main bearings will have to be shimmed or replaced to accomodate the new crank diameter, but all this is still cheaper than a new crank. An alternative to this is to look around on eBay or motorcycle scrap yards (good luck, the CB400A is a rare breed). If these 2 options fail, find an authorized Honda dealer/service center. They should have full schematics of every part, and can tell you what these parts are compatible with (the same crank may have been used in a 400cc engine 5 years later). They may be able to get you the parts, but a new crank may cost more than the bike is worth right now. But by all means, hold on to this machine and keep the original parts in a box if you replace them. These bikes are classic, were only made from 78-80 or 81, and will soon be collectible.