Circa 1974 IH 400 air planter is available from nearby farmer for $500. I know nothing about this unit. He purchased 8 years ago and never used it... the control box which goes in/on the tractor is missing. I wonder if this planter can be made to work economically; do I really need that control box? Also, I have scoured the internet and some people say the only thing about these units is that you have to drive at 4 mph or below. Anyone out there know more?