Doesn't your heater look like that from the back? I have a used one, and it does. I have pictures (including the ones posted a few pages back) of a re-packed (presumed NOS??) heater (which you just re-posted above, emblazoned with the tm9-801 watermark), which is representative of the ones Joe Gopan is selling (or was anyway). I presume that it also is representative of the one he has in his truck. so there are at least three of them, and they also share the common feature of bosses on the front. I have never seen an actual cab heater without the boss. Like you, I have seen a heavily doctored photo illustration of one (or at least a photocopy of one). My point to all this is there are real examples of heaters with bosses that have been seen and are known to exist. The photo illustration would seem to indicate that they MIGHT have existed without a boss.
My point, in the post above, was to address your earlier hypothesis about when bosses were added. I have documentation that the heater shell with bosses first appeared in the 1942 model year (late 1941), and continued to be produced through the 1947 model year. The same manual shows that Harrison produced models specifically designed to fit the 1942 GMC truck. Did they have bosses? At least some of them did. Did they all get defrosters and flaps installed? They did NOT all have defrosters, as shown by the manual. Heaters H-184, 185 and 190 are all noted as designed for 1942 GMC trucks, and none of them had defrosters. (Just a note that the models listed in my previous post DID include defrosters.)
All civilian heaters that I've shown have a couple features that are notably different than the military heaters that you, Joe and I have. Those features include:
Flaps - civilian heaters have them, ours don't.
Extra mounting bolt located near the fan - civilian heaters have them, ours don't.
bottom deflectors - civilian heaters have one, ours have two.
paint - while certainly NOT conclusive, civilian heaters are typically a "hammered" gloss paint, while ours appear to be OD (or certainly "flat").
Even looking back at the previous photos of CJ heaters, it appears that if a heater had internal flaps, it only had one bottom deflector. If there are no flaps, then there are two deflectors. This is consistent with the heater shown in the manual too.
You might have noted that I have taken to calling our heaters (your's, Joe's and mine) "military". Ours all appear to have the same features, including front boss, rear mounting flange, mounting bolt number and locations, number of bottom deflectors and paint.
The photo of the re-pack heater shows that it was re-packed in 1955; indicating that this style of heater was built prior to that. Were they common in either form (bossed or no boss)?? I would suggest no, since so very few are to be found.
This date range can be narrowed a little further by another manual that I have, which is the installation instructions for a Personnel Heater Kit, Ord No. 7354240, which is listed as designed for Chevy 1-1/2 ton 4x4 trucks with commercial cab, and GMC 2-1/2 ton, both open and closed cab trucks. This is a drivers side fender mounted, gasoline fired heater, with ductwork for piping heated air to the cab and windshield of the trucks it is installed in. This manual is dated 1951, and the cover photo, model descriptions, and installation photos are of an open cab CCKW. Also included in the kit were an engine primer installation, and an insulated radiator cover. There is a reference to this kit show here:
http://cckw.org/forum/viewtopic.php?f=23&t=5060I'll keep digging, and hope that someday we can figure out when the "with boss" military heaters were introduced. I'd like to see pics of a "no-boss" heater someday (besides the pic in the manual)!