One other suggestion: you can purchase (via Amazon or elsewhere) 45% vinegar or crystalized citric acid (either of which can be mixed with water to any strength you want). Either of those are very tough on rust. In fact I wouldn't leave either in the block for more than an hour and then flush with clear water. Both of them should be used in a vented area (naturally). If you use the vinegar at full strength you might check around to see what some "experts" suggest.

I use an aluminum radiator, a thermostatically controlled high cfm Spal fan and an extra pusher fan for the A/C unit in front of the radiator. I will tell you the electric fan for the A/C runs on a trinary switch whenever it is on but the main puller fan shuts off when enough air flows through the radiator naturally. One thing is the engine is much quieter without the stock fan. At least mine was notably quieter at all speeds. Good luck!

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end