Aftermarket gears?
Problem is, I can't find any company that makes them.
Just so you know, when I learned how to not break a gear box it was from Joe Liberty. I did exactly what you are doing. I was looking for the 9310 gear set.
A few minutes into the conversation he asked what the issues were. I told him I can't keep third gear in one piece.
He asked about the clutch. When I told him I had a 3 paddle disc and 2400 pounds of plate pressure he told me that he couldn't make a gear that clutch wouldn't destroy.
That's when he schooled me on clutches. Still being a little wobbly on his thinking, I called the guy at Jerico and told him what I was doing.
He said the same thing Liberty said, and that was he couldn't make a gear set to take that either.
The upshot is it's not that the gears are weak or old. The fact is these parts breaking clutches have set back stick racing for decades.
I don't like to see you looking for a unicorn to plow your field when you have a perfectly good draft horse sitting there.
The 833 isn't some weak sister to the Muncie or the T10. There is a reason why they made adapters to put Chrysler boxes behind GM engines.