In all my dealings with my 123 Starters, I've never experienced the starter hanging in the flywheel.
Yes, this starter is extremely similar to a Delco type starter with drive, solenoid and motor.
I expect that you are going to find that the starter primary circuit is the problem, not the starter itself.
To test this, simply connect a voltmeter to the primary wire(the only small wire going to the starter solenoid) and ensure that the voltage is going to zero after you release the key from the start position.
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