I'm sure it work on an original door also, in fact I'll be finding out after the holidays. I have an older 18 1/2 WSM that needs a new latch and I'm going to switch from the old style to the compression latch.
What about some Nomex gasket around the door opening? I have it on the top and sides of my door opening and get a good tight seal. I also put the gasket around the top for the lid. I can definitely tell the difference now in terms of air leaks and controlling the temp.