I remember asking an old fella who rebuilt gearboxes once if he could do an "upgrade" or "heavy duty" rebuild on mine (another brand). His answer stuck with me and I found the logic difficult to fault (and have generally found it correct).
His answer was roughly...."gearboxes in general are designed to certain tolerances and only take certain size parts. But what I could do is rebuild it with the best parts I can source and then tell you it's had a heavy duty "upgrade"if it would make you feel better? lol.
He then explained that the thinking behind buying something and then trying to upgrade to get it to do what you need, is a reasonably good indication that you have bought the wrong car to begin with. Though I don't doubt some might disagree.