Not all fabricators tapered the legs. Some clipped the bottom corners on a 45* angle, some angled as shown in drawings, some did not angle at all.
The first stoves that were not UL Listed were built with this same box with angle iron legs. They were all tested, but there was not testing criteria recognized nationwide until UL became the standardized test. Any lab can test to their criteria for testing. So UL labels have different labs and the Listing number they were tested to on them. For a very short time, this older style was Listed with added shields. The tested model back then was only needed when installed on combustible floors with floor protection, or near combustible walls. When installed in a basement on cement floor, or non-combustible hearth, UL Listing was not necessary. The shields were added to pass clearance tests to stay within temperature specifications. So many fabricators continued to make this unlisted style selling for $100 cheaper when customers did not need the tested model type.
In 1977, there was a revised drawing sent to fabricators with optional shields added to bottom and rear bolted on. When equipped, this made the new optional model a Papa, Mama, or Baby II. This was the first Roman Numeral use. They were not Listed because UL did not become the recognized testing standard until almost 1980. Also the shields were removable, which would not pass testing without being integrally attached. You have one of the first tested models. There were not many of these, since 1980 was the year of the major redesign.
The new Cathedral doors sealed the same way to the same size door seal, just a design change. They also were available with optional brass or nickel plating on the new style doors. This was to compete with so many others copying the Fisher design. No one else added as many options and accessories and promotional items as Fisher. This is what makes collecting their memorabilia interesting and a challenge.
In 1979, the double door stoves were available with optional Cathedral doors with the arched top. The very first use of this style can be found on the XL only made in Utah. So it is unknown if the designer there designed the first arched top doors, or if it was a precursor to the change when all the old style flat top doors became obsolete in 1980. Along with this door design change came a wrap around front corner that no longer used the angle iron corners for legs. For all practical purposes, these bent boxes became known as the UL Listed style box. They also had rear and bottom shields. UL Label was attached to rear shield. Since many fabricators continued making the old style as well, once they went to the Cathedral doors in 1980 it is difficult to date the old style box with angle iron, unlisted with no tag, with the newer doors.
The picture of your tag is cut off at the top. Does it have a model Papa Bear VI on it? The numbering system went from I, then II with added shields, (not on tags or literature, I only know that because I have the revised drawings) to III for double doors in 1979. IV was glass doors, and the VI was the single door Bear Series with non-removable shields designed for UL testing. The testing started in '78 with this manual; (as rare as the stoves) This should be yours. I don't know how many of these exist since this is the original sent to UL to become a part of the Listing. Notice the file number and other internal numbers on the cover where UL filed this. I have paperwork where diagrams were changed, so this may not be the final that was packaged with all the stoves at later dates.