My understanding on gears is... The cast iron gears dampen vibration and noise but steel gears are stronger.
As for gibs.. I had to make some and it was a real learning adventure.
Cutting them from steel stock, tried cold rolled and hot rolled. They curled like a banana. Had to cut it way thick and keep flipping it, machining just a bit off
each side and using force to straighten them up enough to flip for the next pass.
Haven't tried putting them in the oven. That might help!
Cut some from brass. Same problems.
Finally got some in brass and some in steel good enough to scrap flat but even scraping tended to make em curl.
Lots of people will scrape the old gibb and put shims behind it to fit. Nothin wrong with that.
I would have done so but the original gibs were so mis-sized and crappy I deemed em trash.
The brass gibbs I put in my lathe seem to be working fine, haven't had to make any adjustments since installation, but after getting more use on em will pull the slide off and have a good look.
I understand that steel is better than brass but cast iron gibs are the best for low coefficient of friction as well as for dampening vibration.