1948-1952 truck recirculating heater location?

[Vanspeed]

Hi guys,
Have a restored standard recirculating heater for a ‘49 F-1. The truck had a heater it in that was directly in the center under the dash and very crudely installed. I see the knockouts for the fresh air heater next to the battery. That heater has vertical inlet and outlet. The standard has horizontal and that would put the hoses coming out over the battery? Also there are no knockouts anywhere that I can see for the standard heater. Can somebody tell me where the standard heater would have been installed? Last pic shows the vertical knockouts along the side of the battery. Any help appreciated as I can’t find any info or photos showing where this heater mounts.