A Seattle-area source for classic Mustang parts with a worldwide customer base–as well as a number of other auto recyclers–may have to give way for a sewage plant. The Wild West Classic Mustang Ranch, which has been selling used classic Mustang parts to the Ford marque’s dedicated following for decades, will be forced to move along with the other businesses if a final decision to build the pant on the site is made. By midyear, King County (where the facility is located) will make its final decision about building the Brightwater sewage treatment plant, needed to accommodate the region’s growing population. County executive Ron Sims has said he would like the project to be in the Woodinville area because the location has the advantage of space. If the area is selected for a treatment plant, the county expects construction to start in 2005 or 2006. The county is reviewing the project’s environmental impact. But if built, about 20 property owners or businesses — mainly auto wreckers — will have to give up land to make room for the sewage plant, which will cover 106 acres, according to the county. The Wild West Classic Mustang Ranch occupies three of those acres. Filled with about 400 vehicles, vintages 1964 to 1998, this car yard and tiny shop have become magnets for auto enthusiasts worldwide. Mustang lovers in Canada, Australia, South Africa, the United Kingdom, Mexico, and Kuwait have ordered parts. “We’re OK with it, but I wouldn’t want to be the one who has to haul this,” said Matt Penick, 32, a co-owner. He said county officials have been helpful. But he’s concerned about losing business. The county will compensate landowners for any move and will cover business relocation costs. But for this shop — which Penick said is the largest Mustang parts business in the Pacific Northwest — picking up will entail transporting at least 1 million parts. That excludes car frames. “I don’t even want to think about it,” said manager Bob Riddle, 42.