NO-the bell housing of a 390 has the bolt pattern from the FE family of motors,352,360,390,406,427,and 428. The 400 (m) is the same as a 351(m),429, and 460 bolt pattern, They are two completely different patterns.
390 is closer to 400.
.975 you divide 400 by 390.
390
390, 400
400
400
It is 400 and not 390
It is: 400
400
400
400
400