Will take enough air volume to build up and retain the release pressure of the trailer brakes. If no leaks should not take a lot to release them but you need to have enough capacity to keep them released. Don't want them applying while going down the road. Also depends if you are intending to use them to help control trailer with the tractor.

I know Ed Boysun added a compressor and controls to a Challenger tractor to pull B train setup.

Click on pictures 7 and 8 on this page which might give you some ideas.

http://www.boysungrain.com/shop-projects.htm

Years ago I saw 22ft grain trailers pulled locally with JD tractors (40/50 series?) but don't recall how they were setup to handle the air supply. One was with a converter dolly the other was a pintle setup on 3 point quick hitch since it was already set up that way to be pup behind the other one.