as cheap as they may be, it would be a waste to trow a good part away... so try to measure it like in the Bill Fisher book.
but here is another question. can the gears be smoothed out agian? just rub it on a perfectly flat sandingpaper so the gears and housing are flat again? or is the slack on the drivegear and maybe the space between the gear and housing a bigger issue?
I will take a look again as my only examination has been cursory at best, so far. For me, I'm not a cheapskate by any means, even though for me 40 or 50 bucks isn't money I've got growing on trees... it's just purely a matter of not wanting to dispose parts that may be still solid enough for such a project as a STF type of engine.