Hard rubber eagle grips were introduced in 1882, at serial number ~73,000. They continued until 1896, when the eagle-less grips were introduced at serial number ~163,000. That's from memory, so don't quote me on it . . .
Actually, I dug out an old SAA article that appeared in Shooting Times in the early '80s, which had a large chart of dates and serial numbers for introductions, deletions, and other changes during production.