[Chuck78]

66-72 suburbans use a heater core that's 9 1/4 x 2 x 2. Looks like (despite the deceiving pictures), that the best core to try and retrofit if reworking the standard case would be for the 61-63 fresh air heater unit...
...when I get the time!

Have to take into consideration the blower wheel size and fan rpm as well. I wonder if the deluxe heater's fan cage is much larger? That might factor in whether or not this would be worth it, vs. just going with a vintage air unit if it's larger.

EDIT - looks like there is only one blower motor for the two different heaters. Now if I only knew if the blower cage wheels were the same size between the two! Anybody got lots of parts lying around to compare??? I'm thinking maybe this case modification to fit the deluxe fresh air core might be the ticket, and then duct the single outlet to some dash vents that I'd have to add on.