Anyone replaced a downdraft cooktop?

[tarheels]

We have to replace the cooktop in our rental. Of course, it's 12 hours from here and I can't see it to look at it. It's a 30" downdraft. Are all 30" downdrafts the same, so it's just pop the old one out and put the new one in? Or will there be complications in matching up the existing venting with the new top? (Yes, all the models I'm looking at have the vent in roughly the same place as the existing.)