Adam, for what it’s worth, here is a page from the B-26B and C model Flight Manual showing the basic layout of the heating and ventilating.
A30D5380-7332-49DF-8045-FB20B07EB61D by
tanker622001, on Flickr
AF9983BC-4EB6-4989-AF54-08D06FCC354E by
tanker622001, on Flickr
This is basically the same information from a Navy JM-1 Flight Manual
BAC6B568-E490-4124-9EC8-012C0F347361 by
tanker622001, on Flickr
12C37992-AA64-4581-B7A2-76D4F7105B59 by
tanker622001, on Flickr
Here are a couple of pages from the B-26F and G Model Flight Manual showing the area just inside the nose. The second picture shows the initial routing of the heater hose
F867047A-F074-4703-9B40-8B6413E970AB by
tanker622001, on Flickr
B1137E2F-B7FA-4CFF-A282-D09CAC9768EC by
tanker622001, on Flickr