If I put a larger airfilter on my FF would it help cool it down or not

The air filter doesn't really help with cooling. It's there to clean the air the engine needs to mix with the fuel to get the liquid fuel to ignite. A bigger air filter will let the engine suck more air into the carb and allow the engine to 'breathe' better. Then again, a dirty air filter will make the engine run hotter, so a big clean air filter might possibly cool it down. Only one way to find out dude!!

Your best bet is a bigger heatsink. Or if you havent already, cut a hole in the windshield of your body in front of the engine.
A bigger air filter sill only help IF the current one is restricting the airflow. More air in = better combustion + more air flow, which creates more cooling. BUT the engine can only suck in so much air at whatever RPM its runing at, so if it is getting max air flow with the current filter, then a bigger one wont make a bit of difference.
Hope that makes at least some sense...

cut a hole in the body of the truck and get a heatsink, thats the only things i can think of