John, looks like there are some original Halibrands on ebay that might work for a gulf-spec car. They're listed separately (16X14 and 16X10):
eBay Motors: Brand New Halibrand 16X14 Magnesium Sprint - Champ Car (item 140269451116 end time Oct-02-08 09:06:35 PDT)
Do a search for "halibrand" in ebay motors. Perhaps these would work for you?