Sarge I would put a timing light on that thing and make a few chalk marks or a timing TAPE on the balancer and run the engine up to see how much timing is in the setup at 2400 rpm.
Like I said I had the same problem with an engine that wasn't advancing the timing enough at speed. If your timing is GOOD then I'd put the larger fan on there. 238 is about 20* higher than I'd like to see the temp at speed.
Big Jim

professional bovine relocation specialist