Supro Steel Guitars
This actually gets a bit tricky, because you don't have a conventional string-through pickup. You actually have a cover plate from the 1st generation that was re-drilled to accommodate the poles from a 2nd-generation pickup.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 Models
Lollar Supro style pickups are a limited production, under license of Supro USA. Supro Lap Steel Guitar History' title='Supro Lap Steel Guitar History' / Serial X14706. Perhaps the best way to describe this very cool 50s Supro Steel guitar would be to quote the companys original catalog description. We have the Supro 1950s Lap Steel Lap Steel. Sunday, September 22, 2019. The serial number was X85685. The colour is not as intense in real life. This one had what appeared to be original Kluson gold sparkle tuner buttons. A red 1956 one bought in October 2007 for sentimental reasons (because I was born in 1956). The serial number on that one was X64357. Vintage Supro Lap Steel Electric Guitar 1956 w/Hard Case Lapsteel Click to Enlarge Click to Enlarge Click to Enlarge Click to Enlarge Click to Enlarge Click to Enlarge Brand name: Supro, Product type: Lap Steel Guitar, Serial number: X917xx(AD) Inventory number: 1389, Condition: Previously owned in good vintage condition overall.