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Can't say as I've seen a video specifically on this issue. But boxer2valve has a channel on youtube and there are a number of engine related videos...maybe they discuss it there:
Measure diameter and length and post here so others can verify that the pin you found is the bearing retaining pin and not a rocker needle. I once found a pin in the pan of an R80 but it was much larger diameter than the bearing pin.
Snowbum indicates the crankshaft pin is about 11mm long and about 4mm in diameter. Assuming you measurement units are inches, you have about the right length, and your diameter is spot on at 4mm. It's difficult to find any documentation on the size of the rocker arm bearings, but I ran across something which suggested they were 15mm long by 2.5mm diameter. Those dimensions are very different than what Snowbum reported for the roll pin. I suspect that the pin in the crankshaft would of larger diameter in order to take the loads involved. It's easy enough to verify that the rocker arm bearing housing are intact by doing an inspection. Brook Reams has pictures of the rocker arm bearings for his R100RS rebuild here: