Can anyone help me with a Hurst Promatic 2?

I modified a pistol grip handle to fit on a Promatic 2 shifter, but I'm having trouble putting it back together. The main pin (the one that fits in the slot ) won't go in far enough to allow the snap ring to go on. It's sticking out and won't slide in all the way in! Tried tapping and rotating it but it won't buge!
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