Fan that far from the radiator without a shroud is pretty much useless. It will be a challenge to make a shroud to fit this application, but without it even a bigger fan won't help. Also kind of dangerous to work around an open fan. I had one almost take my finger off when I was too young to know better.
Electric fan with its own shroud, or add a shroud to the mechanical fan. Electric fan draws a lot of amps, be sure you have enough alternator.
