Now this is a nice design for a 20B turbo manifold...

They exist. I know ABB has used them on specialized 5 cylinder diesels for
marine applications:

Description:
http://www.rx7club.com/attachment.php?attachmentid=437407&stc=1&d=1311980178
Coden, "Controlled Pulse turbocharging of medium speed 5-cylinder diesel
engines," 2005

 Marc Wiese