Model a Heater

[fourfords]

When I bought my little Roadster earlier this year, it has a 2" hole for a heater in the passenger side of the firewall. I will be looking for the manifold and heater cover here soon. I have learned so far that there are a few manufacturers. I guess my main question is: Will all of the manifolds/Covers line up with the existing hole in the firewall? is this an issue? what else do I need to know before I start spending my hard-earned money? I figure now's the time during the summer to start the search.