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...bars have come a long way since those were made. If it were me, I'd toss the bar along with the stem.

Measure the bar diameter at the insertion point into the stem. Not sure, but I have a feeling it might be different from the current standard. There are a ton of Asian bar and stem combinations floating around in the used parts stream that will work on that.

If you are really attached to the original bar for some strange reason, and are going to toss the stem anyway, just use a pry bar to pry open the clamp end of the stem by inserting it into the slot.