I have two big blocks, both running on synthetic oil. ( I also have some big block F#$ds on synthetic, including my 37ft MH )
I have an electric fan on the 396 with a stock 55 chev rad, and I have never had a problem in the 32 years the fan has been on the engine.
My 454 has a clutch fan, and although I have run Fexalite fiberglass fan, I prefer the clutch fan.
Bob

55 Cameo 396 TH 400 with overdrive
65 Caliente conv
67 BB Caliente conv
67 Mercury 1 Ton
76 GMC 3/4 ton 454ci
84 Buick Turbo Regal