I’m pretty sure it’s a ‘70.
Here is a pic of my Silvertone’s label:
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As best as I can recall, I got it for Christmas in 1970. That’s what my parents recall too. I was in 7th grade and just quit boring piano lessons. It came right out of the Sears wish book. It is possible that it was Christmas ‘71, but we doubt it. By 8th grade I was in a band and annoying the neighbors. Our version of Wipe Out was, well……..
You asked about cracks. Here’s the back:
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Here’s the front:
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I only see a few finish cracks.
This model was also made with a rocker switch. I don’t know if it was the previous or subsequent incarnation.
Anyway, shim the neck to get the action lower, set it up as best you can and it’s a great little bass if your grandson is so inclined.