The basic difference in the older and newer slides is the cut for the safety on the left side of the slide for the older ones. A new slide could be cut for the safety or the safety tip could be ground off. The interior of the back end of the slide is squared rather than rounded but doubt it has any effect as the cocking action is done by the bolt.

A couple of other points - the cocking indicator is in the frame, not the bolt, - and there are at least two reported slids breaking at the rail to body connection. Quality of the newer slides is variable with bolt to slide fit and apparent soft metal in some slides and barrels.

I would suggest you buy an older used slide in VG shape.

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TOMBECK