Todd, when we were still running Stock Honda we’d run about 3-5 events. Figuring about 1.5 hours for a two day and 2 hours for a three day national. Road racing that is. So the 5 hours Josh mentioned is a pretty good guide.
For a 5-6 event season, we’d put a piston in it half way through the season, and of course a new one to start the next season. Every other season we’d put a crank in it.
We only ever broke one piston and that was breaking the engine in!!! Go figure??!! And I never found a crack in any we replaced, so it’s more of an insurance thing. BUT, if a bottom end bearing goes it can make a huge mess!!!
So in your case, I suspect both your motors are ready for a crank and piston. Hope that helps.