I couldn't find a quick reference to the place most of the Impala guys use - 2 different styles.
1. is
http://www.weldcraftwheels.com/ who welds in a section from another wheel
2. is Vaughn machine -
http://www.mkiv.com/techarticles/par...ned/index.html - for an example - that welds in the back half of a wider aftermarket wheel.
3. is
http://internetalternatives.com/wshoppe/wwiden.htm who does wheel widening as well.
I'll defnitely be doing this even if it's just for 10's as 315/35's will easily fit on a 10 and have a good cross section.
Mike