Heritage birds? 300 or even lower. I would also experiment with roasting breast down in like a dutch oven, especially if you don't care about skin. The legs and thighs of a heritage bird will take a little longer than the breast to cook, and if you cook it upside down, the breast will stay WAY...
This!
In addition to resting (at least 2 days on a heritage bird), you have to take into account methods of cooking.
Broiler means a young chicken that can be cooked almost any way. The young meat can take much higher temperatures to cook and so modern roasting methods are high temperature...