I have my first batch of meat birds.
What kind of meat birds do you have? Cornish X, some type of Ranger, or are you growing out dual purpose types?
Right now they are in my largest brooder box in the garage with a heat pad and a brooder heat plate, but they are rapidly outgrowing it. Since it's fall I'm not sure when to put them out.
Mainly out of curiosity how old are they now? That might help on a way forward. You can toughen them up by exposing them to colder temperatures even when they are really young, just give them a warm place to go to so they can warm up when they need to.
What does the facility look like where you will put them when they go out? You need good ventilation but you don't want a breeze hitting them, especially at night.
Our day temps will be in the lower 70s but dipping to low 50s at night. Can they be out at night if I put the heat sources in the sleeping area of their chicken tractor?
My brooder is in the coop, not a tractor, but you can probably move them to that tractor now even if they are really young if you can provide them a warm enough place in the coolest temperatures and a cool enough place in the warmest temperatures. To me the biggest issue with brooding them outside is the temperature swings, I've seen it go from below freezing to the 70's Fahrenheit almost overnight. Your brooder needs to be able to handle that swing.
A photo of the tractor, how many chicks, and their age might help us make suggestions so you can move them out sooner rather than later.
I don't have experience with Cornish X or Rangers, but I'd feel comfortable leaving my dual purpose chicks outside without heat with those temperatures at 4 weeks with good ventilation and breeze protection.