I have never seen that exact FL350 head either. It does remind me of one of the AftershotMotorSpurts models though.
As far as a radiator, I would use a Banshee radiator. It has a vertical configuration if you want to use it in thermosiphon mode and it fits in the cage nicely. You can get brand spanking new heavy duty Banshee radiators for a fair price of around 70 bucks.
As far as fan or no fan, I have ran them in both configurations.
If you plan on running at low speeds or mounting the radiator in an area that will have a restricted air flow, run the fan and a thermostat. I had a thermostat on mine and I think it came on just a couple of times. I wound up changing the fan to an on demand switch. This works nice if you want to cool the top end down quickly after a hard run without the
Engine running.
As far as pump or no pump, I have ran both ways and here is my take on each.....
Pump mode:
Pros: It does make it nice to be able to circulate the water quickly for a fast cool down.
Cons: Unless you install a thermostat into the system, a pump will circulate the water continuously which make warm up time a bit slow. You could configure the pump on a manual switch but there is the chance of forgetting to turn it on. There is also the chance of pump and or switch failure.
Thermosiphon Mode:
Pros: No moving parts and fast warm up of the head.
Cons: The water circulates slowly which will make cooling response time much slower.
Rand