Everyone is going to suggest who they use. Turbo Action, ATI, etc all the big name places are going to give you pretty much the same thing. Call them, tell them what you have and what you want to do, and let them build you a unit. It's simple as that.

If your local guy has Wallies and bracket race wins under his belt, go with them. If not, don't. There is no benefit to going local when it cost $75 to ship a converter anywhere in the country, and the difference can be a round win.