I think.Bob said he only.has a (Myford) lathe and a couple of chucks etc? If so, the rotary table would need to stand vertically on the cross-slide as.he suggests...
It could br done, but I can't see an alternative to milling the flats (other than filing) with a small, delicate cutter in a less than rigid setup - recipe for broken cutters and damaged workpieces!
A local engineering works went from CNC machining hex sockets in parts to rotary broaching, saved upwards of.a.minute per part, lot less breakages of small carbide endmills, they reckon it saved £1 or more per part, £200 a day up in profit...
A rotary broach would.be worth the.time in construction, I think.