Adding a pusher to these old trucks is not for the inexperienced. It would require a drop center axle for openers and having a both a hydraulic and an " air brake system for the rear axle" is not only totally impractical but would be dangerous to boot.
Don't try to re-invent this truck. If it's the old cab look your after then put the cab on a late model chassis with the things you want (disc brakes, etc.) and call it a day. You'll be way ahead of the game and have a drivable and safe vehicle. Don't mean to rain on your parade but your statement makes me very suspicious of where you seem to be headed.
