It looks like a Firing Pin Safety Lever Plunger was introduced into the 2nd gen slides.

Does that mean that if the Plunger was removed, the slide would be functional equivalent to a 1st gen slide?

Driving the question is wondering if removing the plunger from a 459 slide, would it work on a 39 frame?

For inquiring minds, mechanically the answer is yes.

I purchased another slide and removed the plunger. Also installed a Millet series 100 rear sight, 40505, while I was at it.

Function check on the bench is good. Now it's time to get to the range and get the sights dialed in.

Now for some eye candy
This slide is pristine, not a freckle on it. Note the NOS Millet rear sights, and the sweet NOS John Daly grips.