Does anyone know how to change a D320T from a 60 horse power to an 80 horse power in a 933 machine?

Should be able to be done with the rack and rpm settings. Now if you want the extra hp at the same rpm, that might get a little smokey. I expect there were industrial/electric set engines that were setup for that much hp, but you have to realize that there's hp ratings for continuous duty (lowest number) and intermittent (highest number) and some in between.

It just depends on what you'll be doing with the 933. If you were plowing with it, that would likely be continuous work while loading/dozing wouldn't likely be that continuous of a workload. When you get into continuous duty, at max hp, then things like cooling get critical a whole lot faster.

The 80 hp 922 D320T has a full load rpm rating of 2400 rpm vs 1900 on the 933
Rack setting changes from +0.020 to + 0.060
Different governor group 9H3722
Gov. spring 7M7721 or 1S720 (color-gray)
Different turbo # 7M9731

Some engines can be tweeked a little more for HP without other attachments and some require added or different assemblies to do it.What comes to mind as an example is the 1693 - D343 engine as the lower HP engines were just turbocharged and with higher HP engines they were aftercooled to deal with the higher HP. You shouldn,t play with rack settings unless you have a rack setting tool so you know where your at on settings.

If you boost the D320T to 80HP from 60HP in a 933, you're likely to end up, tearing the teeth off the bevel gear and pinion .. and these gearsets are made of unobtainum, I think you'll find.
The bevel gear and pinion are a problem area in the 933 at the best of times .. Cat went to coarse pitch teeth to improve their lifespan, but they are still the weak point in the tractor.