There are competing interests here.
The contractor makes more profit (and keeps the bid lower) if s/he does not pay overtime (assuming a fixed price bid). If the schedule is not tight and you have a large pool of workers who are willing to work just 40 hours, that's the way to go. If the schedule is tight, you can still avoid overtime by having two or three shifts of workers. Again, this assumes you can get enough people willing to work just 40 hours. Union companies usually hire out of the local hall so they don't have to bring workers 6-8 hours away. This makes it easier to get workers who don't insist on OT. Even non-union companies may be able to make a temporary arrangement with the local union to hire people for the one job or use temp services that specialize in trades people. That might be the key to getting sufficient help.
The workers generally want as many hours as possible when that far out-of-town. They want to make a big score and usually don't plan on going home every weekend or even any weekend. When I've worked such jobs. I generally did not go home, my wife came to visit me every couple of weeks and sometimes stayed with me all week. If you are planning on paying overtime, it's a good idea to be flexible on scheduling individuals. Some people will want 70 hours. Some 60. Some 50. Some just 40. Your workers will be happiest if you try to accommodate them. Keep in mind that workers are less efficient when working overtime, especially above 60 hours.
If the GC has a super tight schedule and tells you to bid the job assuming overtime, this makes it easier to get a crew together, and presents an opportunity to make additional profit by bringing in as many workers as possible and minimizing the OT paid. You can keep the overtime at a reasonable level (say 50 hours) and pay out more non-OT hours.