Just for grins, take the fan off and make a highway run. I believe you'll figure out pretty quickly where the noise is coming from. Unless you're running ridiculously low profile tires, the 3.55 rear end you've got already is just about ideal. There's nothing whatsoever wrong with letting a 235, or even a 216 wind up where it's designed to run, as long as the bottom end of the engine and the oil pump is in good condition.
Jerry
Great idea. Nothing wrong with running without a fan as long as prolonged idle is avoided. Especially in the current winter months on a vehicle that's just going down the road and not working. Once up to cruising speed the fan is just along for the ride anyway. I've been down the 1/4 mile many times with the fan in the back seat when a few extra hp were required. Much more recently my Dodge Diesel (with it's sized to do serious work radiator) used to regularly see the fan pulled in November and reinstalled in March. Two reasons, one it got much quitter and two the engine heated up quicker on those Cold days.
I'd definitely say pull the fan and take a drive, just watch the temp gauge.
One last thought, since doing a lot of work insulating the cab along with adjusting the valves to the tighter end of the adjustment range my '51 with original 216 is much nicer on the road at speed. At speed means 60-65 mph. Problem at speed is just not enough motor to stay there with any headwind or uphill grade (no real mountains in Arkansas but lots of big hills in the NW corner) it's far from flat unless you're in the Delta.
Good Luck,
RonR
