Finally removed the S10 front and rear windshield to see how the 55-56 Chevy windshield would fit. I removed the S10 roof and A pillars, too. The curve at the base of the 55-56 windshield is close to that of the S10, but it's off enough that a new base will have to be constructed with the rest of the windshield frame. Cleaning up the S10 windshield opening showed me that my guesstimate of the depth of the 55-56 windshield was off by 3 inches, requiring some rework on the Malibu window frame in the S10 door. I also will need to adjust the angle of the window track in the door to match the side angle of the 55-56 windshield.
Oh well, it's just metal.