Although the term Golden Arches is practically synonymous with McDonald’s, only people who were around before the early ’70s have actually seen a true Golden Arches-style restaurant. That’s because the chain altered its look at about that time, replacing the original design with mansard roofs.

So when director John Lee Hancock asked production designer Michael Corenblith to come up with an original store for “The Founder” — the biopic of McDonald’s founder Ray Kroc, played by Michael Keaton — the only building with arches that remained was in Downey, Calif.

The Weinstein Co. movie, which opens wide Jan. 20, was shot in the Atlanta area, where Corenblith had to build two McDonald’s — the McDonald brothers’ original San Bernardino “octagon” structure, erected on a parking lot in Newnan, Ga., and another, of the Golden Arches variety, constructed 30 miles to the north in Douglasville, in a church parking lot.

The designer spent time researching the look of original McDonald’s restaurants. “We did everything in our power to get these things as correct as we knew how,” he said.

With the discovery of archival images of Kroc’s first Des Plaines, Ill., store, Corenblith was able to get a sense of the buildings’ proportions and dimensions, noting the structures’ “big canted roof, and tilted windows — kind of like an airport tower.”

A search on eBay turned up some blueprints of an original Golden Arches store, designed by original Fontana, Calif.,-based architect Stanley Clark Meston. Corenblith also discovered “a little museum associated with the brothers’ original restaurant in San Bernardino, which also had blueprints.”

But blueprints weren’t the last word. “As you begin to acquire more and more archival information, you find that everything you have conflicts with everything else you have,” he laughs.

Fortunately, the still-existing Downey store was a convenient 45-minute drive from Los Angeles, so Corenblith, along with set decorator Susan Benjamin and costume designer Daniel Orlandi, made several early morning field trips to the venue to quietly make further study.

“It was the second Golden Arches model ever built, after the first one in Phoenix,” Corenblith explains. Because it opened in 1953, it wasn’t part of Kroc’s purchase and therefore not subjected to the early-’70s remodeling of all the franchises that did away with the arches.

“The exterior is virtually unchanged, which gave me a template to work from,” the designer adds. “Just to be able to go and look at one and measure one was an immense leg up for us.”

The Downey restaurant is one-third larger than Kroc’s Des Plaines store that’s represented in the film, so Corenblith had to scale things down. The interior, which the designer drew from operating manuals and archival videos of a Des Plaines store replica, had to fit into a 24-foot-wide space, vs. the 36-foot-wide version in Downey. The biggest challenge: re-creating the Speedee Kitchen — the assembly-line layout that adhered to the brothers’ original design, and was common to all Kroc’s stores.

The kitchen in Corenblith’s set, in fact, was a nearly fully functioning McDonald’s kitchen of the day. “The exhaust fans, the air conditioning vents, the grills, the multi-mixers, the French-fry machines — all that stuff was in operation” and handled by trained background actors, he says. “There’s plumbing and electrical systems, just like in the real world.”

The set was a little too real for local building officials, who required the construction of four-foot-deep columns in concrete to support the classic Golden Arches sign, which acted like a big sail in the wind.

“When you’re building these things on stage, you’re not subjected to the rigors an architect would find out in the real world,” says Corenblith. “But once you start building these structures outdoors and subjecting them to wind and weather, there are high building standards you have to meet.”