Hi again wmjoe. I can't really picture that recess there for manifold clearance for the 272's but perhaps for the larger 279 or 317 ohv. This is the only reason that I can think of but only a guess. Do you have any verification about this?
Bye for now.

 

I'm not sure, but could only guess that it's for clearance of the manifold. The one I'm on, is a '54 F-100. I see the heater hole discrepancy too. One set is for the fresh air, and the other for the recirculating type heaters. I know it doesn't mean much, but it is a neat piece of information, and could be used to correctly identify a truck that is missing many other identifiers. Of course, this is what being an enthusiast is about, finding, and taking note of every detail about what one is interested in.

 

Hi again It would definitely tell the story if one put the cab of a 53 onto a 54-55.

 

You made me run out to the garage and look closer at my firewall.
My 55 has the recess and two heater holes, although it's kind of hard to see the recess in the picture.