You didn't say what make of dyno and what sort of figure that is... Also, what mods you've already done. 73bhp at the rear wheel's absurdly strong for a stock bike, if that's what it was... If the runs were done even a day apart you can get a big difference too, I was once in YPE and someone was complaining that they hadn't hit 160bhp. "Bring it back on a colder day" was the answer :)

I presume your dyno runs were done on corrected figures which allow runs performed on different days to be comparable. Although with a dip in the power as you have described i doubt this would be an issue.

Tight clearances can cause the problem, but more likely cams not being in quite right can be the main cause. Were they done to the spec in the diagram as TSM says?. If not then this is possibly the cause.