If you are using a 400 balancer (ext balance) you will need a 400 flywheel. 400 stick flywheels in stock form are hard to find. Probably have to go with an aftermkt steel one.
If you have the crank internally balanced, you can use a 350 type wheel. But, internally balancing a 400 type crank will cost you more. Last time I had a customer insist on internal balance. He had over $600.00 in a cast crank.
Eight pieces of Mallory metal ($$$$$)plus a lot of labor.