I see what you mean - not familiar with what's out there for the hemi.
Starting with an existing aftermarket 4 bbl., the volume can be increased somewhat with a simple tall spacer, and the runner length extended to get some useful inertia fill (if not an actual tuned length) by just splicing in a section between the flange and the plenum entry, but a complete re-make (changing runner entries and distribution) is a lot of work.
IMHO a side-draft, especially IR (Weber DCOE, Mikuni PHH, Dell'Orto) is easier to design and fabricate than a 4 bbl., because internal plenum shape and volume is less important and easier to control. Also easier to play with the length with flanged stubs, etc.
