Easier breaking is possible, but as long as it's 3 or 4 degree max per keyway, he should be ok. Just make sure there is no slop. If he is trying to run over 100,000 miles then, yeah they will strip or snap. Performance is not longevity.
3500 hasn't told a lot about his cam, or set up- so I didn't pry. But maybe should. If you don't want to share details-it's ok. But what I've caught so far:
Regrind cam, so not as much lift and duration as stock so he is trying to shorten the power band. In doing so it becomes more important to move the range of that power band up or down in rpm to match acceleration rate and gearing. The rule of thumb is 1 degree per 100 rpm. So a 10 degree advance would move his peak torque down 1000 rpm. Colder burn on startup, and intake valve hitting piston is only concearns here.
This helps a lot keeping IP output in lower rpm so high fuel rate is easier. If still running the hx35/40 then a quick spool is going to be required to maximize the stump puller build. It will also help cool the valves better to beat egt. He just looses the top 250 rpm from the engine.
The opposite-a 10 degree retard will cost the lower end but help the easier flow top end rpm and maximize fuel savings if boost is back down to half its peak and a little more egt as the burn gets to the exhaust valves a bit more. Or if he is pouring on the coal at high rpm and able to ramp boost to the peak, like a little fuel kicker (propane or meth wmi) can push his torque curve up closer to the horsepower curve. The danger here is burning valves, increased egt, exhaust valve hit piston.
If we see you hooking up to a tractor sled, I guess we know.
