Emtech Automotive here in Adelaide do it. They take your throttle body and bore it out to 70mm at an incredibly inflated price, which is actually more expensive on an exchange basis than if you just bought a new Yella Terra 71mm throttle body...go figure.
The VN V6 and VN V8 throttle bodies are the same overall, so they can both be bored to the same extent.
65mm is for the V8, I wouldn't be waisting $200-$300 buks on this crap, get ur throttle body cleaned "which you should do when servicing any way",clean ur idle air control for next to nothing and that would be enough,spend the $300 buks on something else for the 5Litre ie roller rockers or something else.
If you are after some cheaper mods go the V8 Throttle Body for the 3.8L buick.