I recently completed in Solidworks the engine block true to Ford blueprints. Having 3D prints made by Shapeways scaled to 16% in acrylic. 1946 to 1948 59 block.
Found out they offer different materials including brass and bronze. I thought it would be in some kind of faux material simulating the real metal, but it turns out they print in investment wax and cast the part. Quite expensive, but there's no other way to get a true to scale block that could be used to make a running engine. 1/4 scale would be a logical choice. With some details deviating from true scale 1/5 could be possible.
I've been a toolmaker, but "discovered" CNC and make parts for my full sized Flathead, patterns, core boxes, castings and finished intake manifolds and heads.
I am not a model engine builder, too old to become one, but would be willing to share my CAD files with a serious builder willing to tackle a true scale Flathead.