As an example, on my Detroits in recreational service levels up to 150ppm
are not unusual. If you run the engines daily you will get MUCH lower
numbers, but the usual "weekend warrior" who doesn't run for a week or two
at a time gets higher numbers on iron, because of start-up wear and
relatively longer time (in clock hours, not engine hours) between changes.
I'd change the blown head gasket (assuming that's where the leak is), make
sure the coolant leak is fixed, look at the bores while you have the head
off, and do some short-interval changes with monitoring.
Oh yeah, don't go do any 100nm offshore trips until you know the engine is
ok too....