If helpful, here are a couple pics

 

You're in for a treat friend. I've done that job a few times. The shaft in question comes out the front of the engine, so the whole front axle, radiator, support, and all that comes off. The front pulley and the front timing cover come off. Then the broken gear can be replaced. And yes, the gear in question is #6 on the list. You will need a bunch of gaskets and seals, as the steering pump and its support will also have to come off. It's a project. I think you should plan on a good pressure washing before starting.

 

Thanks so much! I'm looking forward to taking this on-

 

Alright, if you don't mind another question as I try to wrap my head around the project. Am I correct in understanding that basically I just need to remove the engine cover assembly (part 1 in this New Holland TN65 - STANDARD TRACTOR(09/99 - 12/03) Parts Diagrams)
And you're saying that in order to do that, I need to pull the radiator, fan, support, and axle to get to that? From looking at it, I see that there are a couple bolts I can't access at the bottom of the cover - I assume that's why the support needs to come off? Is it possible to get at all that without taking off the axle itself? That seems like a huge step. (To be honest, this project is at the outer bounds of what feels doable for me, so I'm trying to mentally go through all the steps before going ahead).
And is pulling that front pulley something I can do with a standard 3-jaw puller, or do I need something fancier than that?
Thanks so much for your insight-

 

Getting the cover (item # 1) off and back on requires all the room around it you can get. Trying to do it with the front end support still in place is something I've never tried (and don't intend to) but if that's something you wish to attempt that's your choice. The pulley has threaded holes in it for a harmonic balancer type puller and usually doesn't require all that much effort. The crank has a tapered keyed end so the pulley will pop off.

I can give you the whole play by play description of how I do it if you think you need that. If you plan to "farm it out" to someone else I won't waste my time.

 

Thanks so much, I appreciate it. Waiting for the replacement parts to arrive, but in the meantime, I started taking things apart. If you don't mind, my only question is the with regard to the front axle - seems like a complicated thing to remove. If I were to jack the tractor up so there was little weight on the front end, do you think I can just remove the support (I'm assuming we're talking about the same thing - the single-piece of frame that bolts that bolts to both the rest of the tractor frame and the axle that has the battery sitting on it), without touching the axle itself? I can't really tell, but it seems like the support is the only thing in the way of removing the engine cover, but I guess the concern is that there would be too much weight on the driveshaft, unless the tractor body was properly supported?

Or if not possible, do you have a recommendation on how to do it? Would I do the support, then the axle, or keep them together?

 

What I do is this. Drain the coolant and remove the driveshaft. Strip everything from the support casting (radiator, air filter, all of that) jack the front end up and remove front tires. Put jack stands under the clutch housing and/or oil pan (if it's a cast pan) then remove the support casting axle and all with a cherry picker. I use a couple of light chains bolted to the now vacated radiator bolt holes. Set the support down on the cherry picker frame so the weight is on the frame not on the hoist chain. Usually requires a two by four across the frame legs to do this. Then roll the whole thing straight back far enough to get it out of the way. Then the engine is exposed enough to do what's needed. You can then take an air nozzle and blow off more of the dirt and crap you couldn't get to before.