Les, this is an often misinterpreted piece of Internet folklore. The linked article says that they based the Nikon F prototype on the body of the SP. There are a lot of similarities between the F body and the SP/S-series rangefinders, like the faceted appearance and the location of the wind lever, shutter dial, and release button. But the F body is about 1 cm wider than the S-series rangefinders (SP body width 136mm, from
https://en.wikipedia.org/wiki/Nikon_SP ). It's not the same body casting.
Arguably the SLR that is most like a rangefinder is one of the utterly insane Alpa SLRs that has both SLR viewing and a rangefinder. I've never seen one in person. See
https://en.wikipedia.org/wiki/Alpa-Reflex_Camera and
https://www.mikeeckman.com/2019/06/alpa-alnea-model-7-1952/