Honestly early on is the time to play fast and loose with bringing in birds. This is when you have the least investment and you are trying to bring in various genes.
I don’t agree that the most aggressive birds are the best free rangers. Wild Jungle fowl are the most adapted for being wild but they don’t fight to the death. It makes no logical sense for a young bird to fight to the death before he has gained size and experience. Those game birds that fight to the death were made that way by humans. Wild Red Jungle Fowl don’t do that.
The problem is domestication creates and perpetuates disease but gives up wild traits. Wild birds do great living wild but aren’t tame at all, don’t lay many eggs and don’t have good disease resistance.
Pure Red Jungle Fowl were brought over from India and were raised and released in the Southeast in an attempt to make a wild game bird for the Southeast the same way the Dakotas have Chinese Ringneck Pheasants. Obviously it didn’t work…and the remnants of that project are the Richardson Strain…the only Pure Reds in the US. Those birds are adapted perfectly for living wild in Indianbut not the US. Hatchery “Reds” that sell for $5 each and are said to lay 250 eggs a year are mostly domestic. Real pure Reds are much more expensive.
The most disease resistant birds out there are Egyptian Fayoumi. The University of Ohio has a flock for research and they have been proven resistant not just to Marek’s but even most bacterial and viral infections.
In my mind you want the MOST genetic variation early on to get lots of combinations to pick from. If I was doing it from scratch I’d probably find a very old, semi-feral gamefowl running wild on a farm somewhere and cross those with Fayoumi. Then I’d cross those hens with a pure Grey Jungle Fowl and a pure Ceylon Jungle Fowl and then breed the males back to those mixed hens. At about 6.25% I’d inbreed those lines. At that point I’d start free ranging and pick the survivors to make a breed that might live feral well.