Great Dane excavating co.

[9W Monighan]

That gear stock material is really nice to machine. You may want to put a center hole and use the tail stock for better support. You should be able to hog more off faster.
As far as taking all day; It's a hobby you aren't making any money and its the fun of doing this. I would go with the one piece gear and shaft. Less worry, besides by the time you make a shaft key it bore the gear and broach you will have way more time than just turning the gear stock.