Those three dodgy holes look as if they are cored rather than drilled - that is, they were on the pattern used to make the iron casting, so they are cast, not machined. I'd need to see a closeup of the surface finish to be sure of this.
It looks as if the four pop rivets inside each roller-half are holding the ratchet wheel that those pawls engage. That is, the finely machined ratchet wheel is on a separate part which is riveted on to the cast roller-half.
Can we see a more detailed pic of each end of the axle shaft? I can see the left hand end, where the collar slides on over the key, fairly well but can't see detail on the right hand end. I'd also like to see detail of the collar itself, so we can see how the ring gear drives it. I'm guessing there is something like a spline on the inside of the ring gear and the outside of the collar. A key would be sufficient for a metal gear, but not a plastic one, and the design was intended to use a plastic gear. If my guess is right, you may find you get a replacement collar with your steel ring gear, so a simple key can be used, instead of having to broach an internal spline in the steel gear.
I notice both roller halves have pressed in bronze bushes at each end - I take it these are a close fit on the axle shaft. They will need lubrication.
You could use a dry lubricant on both the pawls and the bushes. In the old days we used stuff called Dri Slide, which was a suspension of graphite powder or molybdenum disulphide powder in a very thin volatile hydrocarbon. You dripped the Dri Slide over the joint line, and the liquid carried the powder onto the bearing surfaces, then evaporated leaving the dry powder behind. That sounds like the right technology, but you might try asking a mower dealer's service technician - sometimes they know a special trick, sometimes they don't. If they propose using anything that leaves a film behind, I'd keep looking. You might also try asking a counter-jockey at a Repco outlet - so far I've found them quite knowledgeable, and they have a good range of fairly exotic products.
So, the little pinion on the pulley-clutch shaft meshes with the ring gear, which is splined to the collar, which is keyed to the axle shaft. The axle shaft rotates with the ring gear, and turns the double pawl-block in the center of the axle. The pawls engage the ratchet wheels riveted to the two roller halves. That gives a positive forward drive, but either roller half can over-run the drive in the forward direction only.
