Hey Bukweet, I could be wrong but,I'm not to sure that a rally center is the same diameter as a stock steel wheel.(Thanks, you gave me somethin' to think about while I was cuttin' my lawn)
If they are not the same you could use four stock wheels. Leave the centers alone and cut the ones to widen at the widest straight section outside the center (Lookin' at the front of the wheel just before it rolls bigger towards the valve stem hole)
Cut the donor wheels back farter on that straight section (just before the area wher the center is welded in)
Weld that wide band onto the the wider cut first wheels.
Here in PA we have a few dirt oval tracks that use steel wheels and there are a couple guys doin' this stuff. If you can't find anybody locally try Pete Paulson or Wheel Smith. look in the back of a street rod magazine. Dah, Do a http://www.dogpile .com search.
Take care,Smokey