1931 Model AA shift lever rotates

[stickshift]

So, I'm new to the forum and new to model AA's. I saw one and liked it so much that I looked for one to buy and picked one up last week. Now I'm getting a crash course in Model AA trucks. My truck is as close to original as can be. It has a 1931 engine, but a C head with three bolt water pump. The issue I'm having is when I test drove it I noticed the shifter lever would spin in a circle. It shifted in all 4 gears, but the lever was all over the place. Yesterday, I pulled the trans tower and was glad to see the gears all in good shape. I used a magnet on a stick and put it deep in the trans sump and didn't see any metal filings or chips. I did notice that the oil was 90w gear oil, but I'll drain it and put in the right stuff. The shifting tower looks like a pin is missing that goes through the pivot ball and into the shifting lever, letting the ball turn on the rod. Can I just use a 1/8" roll pin to fix this? Or, is there a special part? Thanks