So with the 617 in the heep and running for over a year now ive noticed that it will run a bit hotter in 5th gear at say 65mph vs 4th gear at 65mph, and my assumption is the pump just doesnt flow enough at that rpm. so assuming an 8" diameter on the crank pulley and a 7" water pump pulley,

rpm, om617 in 300sd 4th gear @65 mph = ~3102 rpm of wp pulley
rpm om617 in jeep 5th gear @65 mph = ~2569 rpm of wp pulley

swapping pulley to one from a 69 mustang with 289 (only $30 new vs over $100 for smaller unobtainium mb pulley) with 5.875" dia
bolt pattern is the same and the depth is close enough a small shim should line it up np.
rpm om617 in jeep 5th @65 mph = ~3063 rpm of wp pulley

does this sound right?