<VV> exhaust manifold mod improved flow?

[chad c]

It seems that the exhaust manifold is fairly restrictive.  I have thought of cutting the end off (where the exhaust exits).  Then cutting the log open long ways, horizontally.  Then having a good welder weld in another 1/2 inch or so of material.  Basically, increasing the internal volume.   Weld the end back on, then open up the exit port to increase flow there.  
 
Probably a crazy idea, I know.  But I figured I'd ask if anyone has done something similar.  And has it helped flow and performance?  What kind of flaws does anyone see in this idea?  
 
I know what you're probably thinking.  "Just put headers on it".  I can't really go with headers, as I'm building a turbo engine.  I'm going with turbo heads which I am porting.  I've had them machined for 140 manifolds.  I'd like to improve the flow of the 140 manifold if possible.  I don't want to have to custom build header style manifolds for the turbo system.  
  
Chad in Denver
1969 Monza Convertible