Either repairs to the pressure tank system or conversion to a pump are viable. I think it depends on what you want to do with the motor. If you just want to run the motor you might convert it. On the other hand, the pressure tank system is part of the character of the motor so if you are after restoration/preservation you might want to keep it as is.
I suspect there are a couple of safety downsides to the pressure tanks. One, you mentioned, is that the system will retain pressure for a while, so if the motor is tipped without venting the tank fuel might flow into and out of the carb–because the float won’t be able to shut off the gas if tipped too much. The other is that leakage might dump gas vapor into the bilge of your boat. I don’t consider these deal-killers for pressure tanks, but something to be aware of.
