I have a similar setup to yours including a higher output water pump, except that I have a stock 2 core copper radiator, 4 blade fan, and no shroud. When I bought the car it had an electric pusher fan. I saw the same symptoms you describe. The fan was on a switch so I could turn it off and on at will. I found that it had absolutely no effect. As my temps would creep up in city driving I could turn on the fan and they would just continue to creep up. So I took mine off. I'm with George in that I think it may have blocked airflow and made it worse. As purchased my 440 had stock heads & pistons. Since then I have made a few mods to bump up the compression and therefore more heat. The last machinist who worked on my engine is a Mopar guy and a serious drag racer. He suggested running a 160* thermostat. He said to try and run it just a little hotter than necessary to make sure the choke opens. He was working on my engine because I had a detonation issue. Stock C.I. 440 heads are prone to detonation due to the spark plug placement. So keeping the engine as cool as practical pays benefits in preventing detonation problems.
When I put the engine back in the car with the new 160* stat it overheated right away. After a little trial and detective work I noticed that the new stat had an opening that was considerably smaller than my original 180* stat. So with the old 180* stat installed everything was back to normal. Note that this was just last month when we had a warm stretch of 40*-60* days. It still wanted to get a little warm in city driving. So before things get too hot this summer I'll be installing a 3 core aluminum radiator. As noted in a thread on radiators last week the best performing radiators have a fin count of 14 - 16 per inch. All of the folks in this forum who have gone this route have cured their overheating problem. You don't have to hit me in the head more than a few times for good advice to sink in. ;-)
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