"dealer installed style" . . . not listed in factory literature [holdover from AD years? . . I have not seen that style of heater on any USA Advance-Design truck (47-55) - Sorry.
The closest appearance would be the Recirculating Heater in Advance-Design USA trucks (here is an illustration -
the common recirculating heater is at the bottom).
Your links to RPO987641 and RPO987641 are not necessarily a confirmation that GM used the part number with the RPO designation, unless those installation instruction came from an Accessory Installation Manual. My guess is that whoever made those two web pages placed scans of the installation instructions with a top-of-page "label" that was typed into the web page, above the illustration/image. The RPO987641 and RPO987641 designations are not part of the scanned illustration/instructions. I'd be interested in seeing the complete entry in the installation instructions. Yes, I have seen the
Index to that Installation Manual, but it is not a scan of the index.
I am not arguing with you, and, I am not interested in arguing with you. I am only interested in seeing complete original documentation.
Thanks,
