Normally (in either version), the magnets would be held down by the top plate on either side of the coils:
They would not be visible in any of the pics you provided. However, it looks like the top plate has been trimmed and the whole thing pinned to the base plate instead of using the normal mounting screws. Normally, this would not leave room for magnets at all. I'm wondering if they snuck them into the middle of the pickup, in between the coils. If you have a spare piece of steel, I would poke various parts of the pickup and base plate to see if you can feel a magnetic attraction. If my suspicious are correct, you don't need any pickup parts at all (though the coils could always be in need of a rewind).
If you're looking for a plastic cover that hides the pickup, a steel this early wouldn't have come with it.
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Old Frets: the obscure side of vintage instruments.
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Supro Lap Steel Guitar Serial Numbers
Supro Guitars History
It's a Comet, which was in the middle of the Supro steel line. The white knob most likely dates it to 1954 or earlier; the other knob is a replacement. If the serial number plaque is still there (nailed to the back of the headstock), the number can be looked up here. Supro Lap Steel Guitars Supro Amps have become legendary over the decades for their desirable vintage tube amp tones, and have been used by some of the most famous guitarists of all time like Jimi Hendrix, Albert Lee, and Jimmy Page.