I PM'ed iw378, but archive here to help others. I have 2 thermal fan clutches that would work. But anyone can buy cheaper than I could sell w/ shipping.
Hayden 2706 "Made in USA", $27 Amazon, $32 Summit. 5/8"D pilot hole (Mopar).
TorqFlo 922747, 0.75"D pilot hole (GM), but bushing adapter for 5/8"D (Mopar), otherwise same dimensions as above. Made in China". $43 Autozone, $49 ebay.
Nice that U.S. made Mopar parts are cheaper for once. I think thermal fans (bi-metal spring) are better than simply "viscous".
My clutch fan is Hayden 3618, 6 blades, 18"D and fits tight on above clutches. Specs <250 cu in engines and <4000 rpm, so "6 cyl", though it would work on a V-8. An older 318 clutch fan I have has 7 wider blades, 18"D. The rpm spec might be confused. The box cover shows a flex fan (most PN's on back), but 3 clutch fans like mine are listed. They have solid aluminum blades, so rpm rating may not apply. Google finds GM guys who used it on a V-8 w/ no problems. $24 O'Reillys. For a true "V-8" clutch fan, might require JY.