Not a retrofit from something else. Brian Littler produced the manifolds and also manufactured a complete CB450 rolling chassis called a "Littler Honda". My recollections from 50 or so years ago are, it was a pretty nice bike with a nickle plated frame and equipped with top shelf bits like Ceriani suspension. The magazine article the photos are from, described the whole lashup in some detail. I believe that Brian lived in South Aftrica. Awhile back, I'd heard Brian (or someone) was going to bring the manifolds back into production, but never saw anything.
Pat