Don't know about Monogram, you ARE talking about the Offenhouse front engine, right? It was around that time period, along with the "midget racer", maybe as early as '54 and among Monogram's earliest kits.
Aurora also had some vintage Indy winners from the 1920s on. I think that they might have had an Offy as well.
-- John The history of things that didn't happen has never been written. . - - - Henry Kissinger