It looks to me as if you would have needed to make an external gear anyway, to attach to the nylon internal gear and thus produce a complete moulding pattern you can use for making moulded plastic gears.
Of course if it will only be used as a pattern you will be hand-filling it with automotive bog, so it does not have to be visually perfect or structurally sound prior to adding the bog, but it does have to run perfectly true, which can be a challenge with hand-filed parts.
I think for 60 teeth I'd have taken the trouble to put it on the rotary table and drill a hole where the gap between each pair of teeth had to be, then only file the teeth to final shape. I'd use a simple triangular file on the filing machine, plus a depth-stop, rather than hand-file so many teeth. The reason to drill the holes with a rotary table initially, then machine-file each tooth to a depth stop, is to give it the best chance of running perfectly true.
