I Run a electric fan on my 66 with a 351 headers etc. No problems at all I run it off a tempature switch so it comes on automatically.Plus I have a over ride switch in the car so I can just switch it on. My fan is wired through a relay which is a must for the big draw of a electic fan.Most new cars run eletric fans as well
for milage etc.Im sure there is pros and cons of each. For instance and electric fan should put less force on your water pump bearings and if you get sucked into a eletric fan Im sure it would stop unlike a mechanical fan.Bottom line I think it is a matter of preferance.