So get rid of the lower and upper altogether. A complete wood stock with a sheet metal inner frame to fit the trigger components and a more classically styled upper to hold the barrel and BCG that fits into the wood stock.
Totally doable, not particularly complicated. Just a bunch of parts to fabricate.
The only issue I see is the AR bolt carrier travels directly backwards, intot he straight AR stock. Whereas most classic rifle stocks are angled downward in relation to the bolt. So it would take some design work to figure out where the bolt goes when cycling. Though there's ways to deal with that.