Can you safely test run a 1969 Johnson 115 hp outboard motor which is off the boat?

As long as you can secure the motor to something that will stand up to the engine's power, and you can get water into it so it won't melt, you can safely run an outboard off the boat. Unfortunately, the "securing the engine" part will hold you back - 115-horse engines will flip over any garbage can, oil drum, wading pool etc., you might come up with. Your best bet would be to take the outboard to a boat dealer and have it tank tested.