2200 cfm is not going to cut it on a big block. I had a similar problem with my 440 and went down the same road as you, new aluminum rad, new stat, water wetter, new clutch fan, none of it worked.
my problem was at idle. even moving at 10-20 mph it would cool right down. I ended up installing a flex fan. I know everyone is down on them, but they cool very well. I used my old electric as an aux "pusher' on the front of the rad.

I'd say your idea about spal fans is a good one. when it comes to fans, either OEM or Spal.
If you run a clutch setup, the MP one is way too "long" at least it was on my charger. I bought a short one from bob mazzoliniracing.com. it was expensive, @80 bucks, but I didn't know any better. members here found a parts store one that's way less money. I never got around to installing mine, so I don't know how it worked.