oldsewnsew

So I'm missing a bit off the top of this Wilcox & Gibbs. Can anyone tell me the overall length of the needle bar, or shoot a pic next to a rule. I think I can modify the "hacked" part. There is a notch, which holds a little rectangular thing with a leaf spring. Mine also has that little post mushed on the top and I think thread goes thru?
a pic of mine.
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What it should look like.
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And what does that leaf spring and rectangular piece do?
Thanks, befuddled and betwixt